HK1090212B - Controlled supersposition coding in multi-user communication systems - Google Patents

Description

Controlled superposition coding in multi-user communication systems

Technical Field

The present invention is directed to improved methods of encoding and transmitting in a wireless communication system, and in particular to improved methods using controlled superposition coding suitable for use in, for example, a multi-user communication system.

Background

Superposition coding in a communication system will be described. A multi-user communication system includes several transmitters and receivers in communication with each other and may use one or more communication methods. Generally, multi-user communication methods can be classified into one of two cases:

(a) a single transmitter communicating with several receivers, commonly referred to as a broadcast communication method, an

(b) Several transmitters communicate with a common receiver, which is commonly referred to as a multiple access communication method.

In the communication and information literature, the broadcast communication method is commonly referred to as a "broadcast channel". The "broadcast channel" refers to each physical communication channel between a transmitter and a plurality of receivers and communication resources used by the transmitter for communication. Similarly, the multiple access communication method is commonly referred to as a "multiple access channel". The "multiple access channel" refers to a physical communication channel between a plurality of transmitters and a common receiver, and communication resources used by the transmitters. Broadcast communication methods are commonly used to implement downlink communication channels in typical cellular wireless systems, while uplink channels in such systems are commonly implemented using multiple access communication methods.

The transmission resources in a multi-user communication system can typically be represented in time, frequency or code space. Information theory shows that in both broadcast and multiple access scenarios, the capacity of the system can be increased more than other communication techniques. In particular, the capacity of the system can be increased more than other communication techniques by transmitting to a plurality of receivers simultaneously in the case of a broadcast communication method or by allowing a plurality of transmitters to transmit simultaneously in the case of a multiple access communication method in the same transmission resource. In the case of the broadcast communication method, a technique for simultaneously transmitting to a plurality of users in the same transmission resource is also referred to as "superposition coding".

See the discussion below of transmission techniques for use in broadcast communication methodsThe advantages of superposition coding will be apparent. Consider a single transmitter communicating with two receivers whose channels may be defined by an ambient Gaussian noise level N₁And N₂Is described wherein N is₁＜N₂I.e. the first receiver has a stronger channel than the second receiver. Assume that the communication resources available to the transmitter are a total bandwidth W, and a total power P. The transmitter may employ several strategies to communicate with the receiver. Fig. 1 is a graph 100 depicting the achievable rates in the broadcast channels of first and second users under three different transmission strategies. The vertical axis 102 represents the velocity of the stronger receiver and the horizontal axis 104 represents the velocity of the weaker receiver. Line 106 represents the achievable speed of the Time Division Multiplexing (TDM) strategy. Line 108 represents the achievable rate for a Frequency Division Multiplexing (FDM) strategy. Line 110 represents the achievable rate for the highest capacity.

First, consider a strategy in which a transmitter multiplexes between two receivers in time, allocating all of its resources to one receiver at a time. If the fraction of time it takes to communicate with the first (stronger) receiver is represented by a, it can be shown that the achievable speeds of both users satisfy the following formula.

The speed achieved by the above equation as the fraction of time spent serving the first user, a, varies is represented by the straight solid line 106 corresponding to "TDM" shown in fig. 1.

Now consider another transmission strategy in which the transmitter allocates a certain portion of the bandwidth, β, and a portion of the available power, γ, to the first user. The second user gets the remainder of the bandwidth and power. After the portions are allocated, the transmitter communicates with both receivers simultaneously. Under this transmission strategy, the velocity region can be characterized by the following formula.

The velocities achieved by the above formula are visualized from the dashed curve 108 corresponding to the "FDM" projection shown in fig. 1. It is clear that the strategy of allocating the available power and bandwidth in an appropriate manner between two users outweighs the time separation of resources. However, the second strategy is still not optimal.

The supremum of the achievable speed area under all transmission strategies is the broadcast capacity area. For the case of Gaussian noise level, the region is characterized by the formula

And is depicted by the dotted curve 110 corresponding to "capacity" shown in fig. 1.

Consists of IT-18 (1): thomas Cover in the IEEE information theory of 214, 1972, broadcast channel, t.m. coverage, states that a communication technique known as superposition coding can reach this capacity region. In this technique, signals to different users are transmitted using different powers in the same transmission resource and superimposed on each other. The gain achievable by superposition coding exceeds any other communication technique that requires sharing of transmission resources between different users.

The basic concept of superposition coding is shown in fig. 2. Fig. 2 is a diagram 200 showing a high power QPSK signal and a low power QPSK signal superimposed on the high power QPSK signal. The vertical axis 202 represents the Q-component signal strength and the horizontal axis 204 represents the P-component signal strength. Although the example of fig. 2 employs QPSK modulation, the choice of modulation settings is not limited and, in general, other modulation settings may alternatively be used. Furthermore, the example of fig. 2 outlines a typical situation for two users, and this concept can be generalized and applied to multiple users in a simple manner. Assume that the total transmit power budget of the transmitter is P. Assuming that the first receiver, referred to as the "weaker receiver", observes a large channel noiseAcoustically, and the second receiver, referred to as the "stronger receiver," observes less channel noise. Four circles 206 filled with a pattern represent QPSK constellation points that will be transmitted at high power (better protected), (1- α) P, to a weaker receiver. At the same time, the QPSK constellation is also used to deliver additional information to the stronger receiver at low power (less protected), ap. In FIG. 2, numerical valuesThe arrow 208 of (a) indicates a high transmission power, andarrow 210 indicates a low transmit power. The actual transmitted symbols of the two high and low power signals are combined, represented in the figure as a blank circle 212. The key concept expressed by this figure is that the transmitter communicates with both users simultaneously using the same transmission resources.

The receiver strategy is simple. The weaker receiver observes a high power QPSK constellation with a low power signal superimposed on it. When a weaker receiver decodes a high power signal, the SNR experienced by the weaker receiver may not be sufficient to analyze the low power signal, so the low power signal appears as noise and slightly degrades the SNR. On the other hand, the SNR experienced by the stronger receiver is sufficient to analyze both the high and low power QPSK constellation points. The strategy of the stronger receiver is to first decode the high power points (which are intended for the weaker receiver), remove their effect from the composite signal, and then decode the low power signal.

Based on the foregoing discussion, it should be appreciated that there is a need for variations and/or modifications of superposition coding concepts that may be used to more efficiently use air link resources in broadcast and/or multiple access communication systems. In a wireless communication system with multiple users, there will be different channel qualities for each user at any given time. Methods and apparatus that depict different receivers and transmitters as being relatively weak/strong with respect to each other and allow these relative classifications to change over time may also be useful. A method and apparatus for scheduling and power control that opportunistically uses these differences and applies superposition coding methods may increase system capacity. New implementations using superposition coding methods may require methods of communicating information between the transmitter and the receiver about the superposition coding, e.g., such as temporary weaker/stronger allocation information. It would be advantageous to minimize possible overhead between multiple communication channel portions, e.g., an assignment channel portion and a traffic channel portion, and/or to combine or concatenate the methods of communicating the time domain assignment indications.

Disclosure of Invention

The present invention is directed to a new and novel method of using superposition coding in a communication system, such as a multi-user communication system. Superposition coding occurs in the downlink and/or uplink. Superposition coding, according to the invention, occurs in the case where the downlink is transmitted from the base station to different wireless terminals using the same communication resources, e.g. simultaneously using the same frequency. Superposition coding, according to the invention, occurs in the case where the uplink is transmitted from different wireless terminals to the base station using the same communication resources. In the uplink case, the signals combine in the communication channel, causing one transmission to be superimposed on another. A device receiving the superimposed signals, such as a base station, recovers the two signals using a superposition decoding technique. The assignment of channel segments to multiple wireless terminals is controlled by the base station in order to obtain the benefits of superposition. Also, in the case of the downlink, the transmission power level is controlled by the base station so that there is a large difference in the received power level to facilitate superposition decoding. In the uplink case, the transmit power level is controlled by wireless terminals sharing the same uplink communication resources (e.g., time slots and frequencies) to confirm that signals received from different devices at the base station will have different receive power levels to facilitate superposition decoding.

In various embodiments of the present invention, a base station maintains information regarding the quality of the communication channel between various wireless terminals and the base station. The communication channel segments are assigned to two or more wireless terminals with at least a minimum difference, e.g., a 3, 5 or 10dB difference, in the quality of the wireless terminal communication channel from the base station in the downlink case or the quality of the communication channel to the base station in the uplink case. The channel assignment is transmitted to wireless terminals that will share the traffic channel segment. The assignment conveys which wireless terminals will be using a communication channel segment at the same time and which assigned device will transmit (in the uplink case) or receive (in the downlink case) strong or weak signals. The assignment message may be transmitted as a superimposed signal.

For simplicity of description, this document assumes that two signals are superimposed to form one superimposed encoded signal. However, more than two signals may be superimposed. The invention is applicable to the case of superimposing more than two signals to form a superposition coded signal.

Therefore, two signals of the superposition coded signal are referred to as a strong signal and a weak signal, respectively, where the strong signal uses high reception power and the weak signal uses low reception power. When two wireless terminals share the same communication resources, a terminal with a better channel state is referred to as a stronger user and a terminal with a worse channel state is referred to as a weaker user. In some embodiments, a given wireless terminal may be a strong user when it shares resources with another wireless terminal, and may be a weaker user when it shares resources with a third wireless terminal.

In the case of multiple uplinks, the stronger user will be assigned to operate transmitting signals that will be received by the base station as strong signals, and the weaker user will typically be assigned to operate transmitting signals that will be received by the base station as weak signals. This avoids excessive interference to other base stations or the need for excessive peak transmit power from the wireless terminal. In those cases, the stronger user is also referred to as the stronger transmitter and the weaker user is also referred to as the weaker transmitter.

In the case of multiple downlinks, a stronger user operation will be assigned to receive the weak signal, and a weaker user operation will typically be assigned to receive the strong signal. This helps to improve the link reliability for weaker users while not wasting power for stronger users. In those cases, the stronger user is also referred to as the stronger receiver and the weaker user is also referred to as the weaker receiver.

Channel assignments transmitted to wireless terminals that will share a traffic channel segment may also be made using superposition coding. Note that channel allocation is typically done by the base station and is transmitted in the downlink. Thus, the assignment sent to the stronger user is transmitted using the weak signal and the assignment sent to the weaker user is transmitted using the strong signal. Thus, if a wireless terminal is aware that its assignment is from a strong signal, e.g., its terminal identifier is transmitted by a strong signal, the wireless terminal knows that it is considered by the base station as a weaker user, i.e., a weaker transmitter in the case of an uplink traffic channel assignment to the wireless terminal or a weaker receiver in the case of a downlink traffic channel assignment to the wireless terminal. Similarly, if a wireless terminal is aware that its assignment is from a weak signal, the wireless terminal knows that it is considered by the base station as a stronger user, i.e., a stronger transmitter when the wireless terminal is assigned an uplink traffic channel or a stronger receiver when the wireless terminal is assigned a downlink traffic channel.

Superposition coding may be used in an opportunistic manner in accordance with the present invention. That is, superposition coding may be used when there are wireless terminals with sufficiently different channel conditions that they can be used to share a communication channel portion in pairs. In the case where a sufficient difference in the reception power level cannot be achieved, for example, due to an insufficient difference in channel state between devices or an insufficient transmission power capability, the wireless terminals are not designed to share the transmission section. In this way, the superposition is used for transmit slots where it is likely to produce reliable results due to sufficient received power level differences, but is likely to be unreliable if not.

Numerous additional features, benefits and advantages of the present invention will be apparent in view of the detailed description which follows.

Drawings

Fig. 1 depicts a graph showing the achievable rates in a broadcast channel for a first user with a stronger receiver and a second user with a weaker receiver under three different transmission strategies.

Fig. 2 shows an example of superposition coding using QPSK modulation.

Figure 3 illustrates an exemplary communication system in which the apparatus and methods of the present invention may be implemented.

Figure 4 illustrates an exemplary base station implemented in accordance with the present invention.

Figure 5 illustrates an exemplary wireless terminal implemented in accordance with the present invention.

Figure 6 shows a typical traffic channel segment.

Figure 7 shows a typical allocation and traffic segment.

Fig. 8 shows a typical downlink traffic segment and a typical uplink acknowledgement segment.

Figure 9 illustrates an exemplary communication system implemented in accordance with the present invention.

Fig. 10 shows superposition coding in a multiple access channel in accordance with the present invention.

Fig. 11 illustrates superposition coding used in broadcast assignment and broadcast traffic channels in accordance with the present invention.

Fig. 12 illustrates superposition coding used in broadcast assignment and multiple access traffic channels, in accordance with the present invention.

Fig. 13 shows superposition coding used in broadcast traffic and multiple access acknowledgment channels, in accordance with the present invention.

Fig. 14 shows superposition coding used in multiple access traffic and broadcast acknowledgment channels, in accordance with the present invention.

Fig. 15 illustrates an exemplary embodiment of the present invention that uses superposition coding on the common control channel.

Fig. 16 illustrates an exemplary uplink signal on the same channel segment and is used to illustrate an exemplary embodiment of a received power target in accordance with the present invention.

Fig. 17 is a flow chart illustrating steps of an exemplary method performed by a base station in an exemplary embodiment.

Fig. 18 is a flowchart illustrating steps of an exemplary method performed by a wireless terminal in an exemplary embodiment.

Detailed Description

As described above, the present invention is directed to a new and novel method of using superposition coding in a communication system, such as a multi-user communication system. Superposition coding occurs in the downlink and/or uplink. Superposition coding, according to the invention, occurs in the case where the downlink is transmitted from the base station to different wireless terminals using the same communication resources, e.g. simultaneously using the same frequency. Superposition coding, according to the invention, occurs in the case where the uplink is transmitted from different wireless terminals to the base station using the same communication resources. In the uplink case, the signals combine in the communication channel, causing one transmission to be superimposed on another. A device receiving the superimposed signals, such as a base station, recovers the two signals using a superposition decoding technique. The assignment of channel segments to multiple wireless terminals is controlled by the base station in order to obtain the benefits of superposition. Also, in the case of the downlink, the transmission power level is controlled by the base station so that there is a large difference in the received power level to facilitate superposition decoding. In the uplink case, the transmit power level is controlled by wireless terminals sharing the same uplink communication resources (e.g., time slots and frequencies) to confirm that signals received from different devices at the base station will have different receive power levels to facilitate superposition decoding.

Fig. 3 illustrates an exemplary wireless communication system 300 implemented in accordance with and using the methods of the present invention. In accordance with the present invention, exemplary wireless communication system 300 opportunistically uses controlled superposition coding methods on the uplink and downlink channels. The exemplary wireless communication system 300 is a spread spectrum OFDM (orthogonal frequency division multiplexing) multiple access system. Although a typical OFDM wireless communication system is used in this application for the purpose of explaining the invention, the scope of the invention is broader than the examples and the invention can be applied to many other communication systems in which controlled superposition coding is also employed, for example, CDMA wireless communication systems.

The system 300 includes a plurality of units: cell 1302, cell M304. Each cell (cell 1302, cell M304) includes a Base Station (BS) (BS 1306, BS M308), respectively, and represents a radio coverage area of the base station. The BS 1306 is connected to a plurality of end nodes (EN (1)310, EN (x)312) via wireless links (314, 316), respectively. The BS M308 is connected to a plurality of end nodes (EN (1 ') 318, EN (X') 320) via wireless links (322, 324), respectively. End nodes 310, 312, 318, 320 may be mobile and/or fixed wireless communication devices and may be referred to as Wireless Terminals (WTs). A mobile WT is sometimes referred to as a Mobile Node (MN). MNs may move throughout system 300. BS 1306 and BS M308 are connected to network node 326 via network links 328, 330, respectively. Network node 326 is connected to other network nodes and the internet via network link 332. Network links 328, 330, 332 may be, for example, fiber optic cables.

Fig. 4 is an illustration of an exemplary base station 400 implemented in accordance with the present invention. Exemplary base station 400 may be a more detailed illustration of any of base stations 306, 308 of fig. 3. The base station 400 includes a receiver 402, a transmitter 406, a processor 410, an I/O interface 412, and a memory 414 coupled together via a bus 416 over which the various elements may exchange data and information.

The receiver 402 is coupled to an antenna 404 through which the base station 400 may receive uplink signals from a plurality of Wireless Terminals (WTs) 500 (see fig. 5). Such uplink signals may include, in accordance with the present invention, uplink traffic signals transmitted by different wireless terminals 500 on the same traffic segment that may be superimposed over the air, and/or acknowledgement signals transmitted by different wireless terminals on the same acknowledgement segment that may be superimposed over the air. Receiver 402 includes a plurality of demodulation modules, demodulation module 1418, demodulation module N420. In some embodiments, the demodulation modules 418, 420 may be part of a decoder module. The demodulation modules 418, 420 are connected together. Demodulation module 1418 may perform a first demodulation on the received superimposed signal to recover a high power or well protected signal. The demodulation information may be forwarded from demodulation module 1418 to demodulation module N420. Demodulation module N420 may remove the high power or well protected signal from the received superimposed signal and then demodulate the low power or less protected signal. In some embodiments, a separate receiver 402 and/or a separate antenna 404 may be used, e.g., a first receiver for high (received) power or well-protected uplink signals and a second receiver for low (received) power or less protected uplink signals.

The transmitter 406 is coupled to an antenna 408 through which the base station 400 may transmit downlink signals to a plurality of wireless terminals 500. Such downlink signals may include superimposed signals, such as a composite of two or more signals on the same channel portion, each signal in the composite being at a different transmit power level and each signal intended for a different wireless terminal. In accordance with the present invention, superimposed downlink signals can be opportunistically transmitted on the assignment segment, on the downlink traffic signals, and/or on the acknowledgement segment. Transmitter 406 includes a plurality of modulation modules, modulation module 1422, modulation module N424, and a superposition module 426. Modulation module 1422 may modulate a first set of information into, for example, a high power or well protected signal, and modulation module N424 may modulate a second set of information into a low power or less protected signal. The superposition module 426 combines the high power or well protected signal with the low power or less protected signal so that a composite signal can be generated and transmitted on the same downlink portion. In some embodiments, multiple transmitters 406 and/or multiple antennas 408 may be used, e.g., a first transmitter for high power or well protected downlink signals and a second transmitter for low power or less protected downlink signals.

I/O interface 412 is an interface that provides a connection for base station 400 to other network nodes, e.g., other base stations, AAA server nodes, etc., and to the internet. Memory 414 includes routines 428 and data/information 430. The processor 410, e.g., a CPU, executes the routines 428 and uses the data/information 430 in memory 414 to operate the base station 400 in accordance with the methods of the present invention.

Routines 428 include communications routines 432 and base station control routines 434. Base station control routines 434 include a scheduler module 436, wireless terminal power control routines 438, transmit power control routines 440, and signaling routines 442. Scheduler 436 includes a downlink scheduling module 446, an uplink scheduling module 448, and a relative user strength matching module 450. WT transmit power control routine 438 includes a received power target module 452.

Data/information 430 includes data 454, wireless terminal data/information 456, system information 458, downlink assignment messages 460, downlink traffic channel messages 462, received acknowledgement messages 464, uplink assignment messages 466, uplink traffic channel messages 468, and acknowledgement messages for uplink traffic 470.

Data 454 includes user data, e.g., data received from WTs over wireless links, data received from other network nodes, data to be transmitted to WTs, and data to be transmitted to other network nodes. Wireless terminal data/information 456 includes a plurality of WT information, WT 1 information 472, WT N information 474. WT 1 information 472 includes data 476, terminal Identifier (ID) information 478, received channel quality report information 480, segment information 482, and mode information 483. Data 476 includes user data received by BS400 from WT 1 intended for a peer node of WT 1, e.g., WT N, as well as user data intended for transmission from BS400 to WT 1. Terminal ID information 478 includes a base station assigned ID used to identify WT 1 in communications and operations with BS 400. The received channel quality report information 480 includes downlink channel quality feedback information such as SNR (signal to noise ratio), SIR (signal to interference ratio). Mode information 483 includes information indicating the current mode of WT 1, e.g., on state, sleep state, etc.

Segment information 482 includes a plurality of segment information sets corresponding to channel segments assigned to WT 1, segment 1 information 484, segment N information 486. Segment 1 information 484 includes segment type information 488, segment ID information 490, coding information 492, and relative strength indication information 494. The segment type information 488 includes information for identifying the type of the segment, such as an assignment segment for uplink traffic, an assignment segment for downlink traffic, an uplink traffic channel segment, a downlink traffic channel segment, an acknowledgment channel segment corresponding to the uplink traffic channel segment, and an acknowledgment segment corresponding to the downlink traffic channel segment. Portion Identifier (ID) information 490 includes information for identifying a portion, e.g., information identifying a frequency, time, duration, and/or specification associated with a portion. The coding information 492 includes information identifying the type of coding and/or modulation used for the portion. Relative strength indicator information 494 includes information indicating the specified WT relative strength for purposes of communication on the segment. In some embodiments, the relative strength indicator information 494 includes information identifying the WT as a weak or strong WT for purposes of communication on the segment.

System information 458 includes tone information 495, modulation information 496, timing information 497, transmit power model information 498, and receive power target model information 499. Tone information 495 includes information identifying tones used in hopping sequences, channels, and/or segments. Modulation information 496 includes information used by BS400 to perform various modulation and/or coding schemes such as, for example, coding rate information, modulation type information, error correction code information, and the like. Timing information 497 may include timing information for hopping sequences, superslots, pauses, durations of channel segments, and timing relationships between different types of channel segments, such as between assignment segments, traffic channel segments, and acknowledgement channel segments. Transmit power model information 498 may include information specifying a model for distinguishing between strong signal transmit power levels and weak signal transmit power levels, where two signals are transmitted as one combined superimposed signal on the same channel portion in accordance with the present invention. Received power model target information 499 may include information such as a look-up table for specifying a model for controlling WT transmit power to transmit at an appropriate power level to achieve a received power target at BS400 for uplink channel segment signals. In some embodiments, the received power model target for a wireless terminal is a function of the code rate and the class of the user (wireless terminal) as a strong or weak user (wireless terminal). In such an embodiment, the received power targets between the strong and weak classifications may differ significantly, for example, by a value of > 3dB, such as 10dB, for the same code rate.

Downlink assignment messages 460 include assignment messages used to notify a WT terminal that it has been assigned a downlink traffic channel segment. Downlink assignment messages 460 are transmitted by BS400 to WTs on downlink assignment channel segments. In accordance with the present invention, multiple downlink assignment messages may be transmitted to multiple WTs on the same assignment segment using controlled superposition coding. Downlink traffic messages 462 include data and information, e.g., user data, transmitted from BS400 to WTs on downlink traffic channel segments. Downlink traffic channel messages 462 may be transmitted to multiple WTs on the same assignment segment using controlled superposition coding in accordance with the present invention. Received acknowledgement messages 464 include acknowledgement signals from WTs to BS400 indicating whether the WTs successfully received data/information on the assigned downlink traffic channel segment. Acknowledgement messages 464 may be transmitted to BS400 by multiple WTs, e.g., widely differing received power target levels, on the same assignment segment and signals may be superimposed in the air link in accordance with the invention.

Uplink assignment messages 466 include assignment messages used to notify a WT terminal that it has been assigned an uplink traffic segment. Uplink assignment messages 466 are transmitted by BS400 to WTs on downlink assignment channel segments for assigning uplink channel segments. In accordance with the present invention, multiple uplink assignment messages may be transmitted to multiple WTs on the same assignment segment using controlled superposition coding. Uplink traffic channel messages 468 include data and information, e.g., user data, transmitted from WTs to BS400 on uplink traffic channel segments. Uplink traffic channel messages 468 may be transmitted to BS400 by multiple WTs, e.g., with widely differing received power target levels, on the same assignment segment, and signals may be superimposed in the air link in accordance with the invention. Acknowledgement messages for uplink traffic 470 include acknowledgement signals transmitted from BS400 to WTs indicating whether or not BS400 successfully received data/information on the assigned uplink traffic channel segment. In accordance with the invention, acknowledgement messages 470 for multiple uplink traffic may be transmitted to multiple WTs on the same acknowledgement segment using controlled superposition coding.

Communications routines 432 is used to control the base station 400 to perform various communications operations and implement various communications protocols. The base station control routines 434 are used to control the operation of the base station 400, such as I/O interface control, receiver 402 control, transmitter 406 control, and to perform the steps of the method of the present invention. The scheduler module 436 is used to control the scheduling of transmissions and/or communication resource allocation. The scheduler module 436 may act as a scheduler. Downlink scheduling module 446 schedules WTs to downlink channel segments, e.g., downlink traffic channel segments. Downlink scheduling module 446 may opportunistically schedule multiple WTs to the same downlink segment, e.g., the same downlink traffic channel segment. The uplink scheduling module 448 schedules WTs to uplink channel segments, e.g., uplink traffic channel segments. The uplink scheduling module 448 may opportunistically schedule multiple WTs to the same uplink segment, e.g., the same uplink traffic channel segment. In some embodiments, the opportunistic scheduling and classification of multiple users as weaker/stronger users in some corresponding downlink and uplink segments may be correlated and follow a predetermined method known to both the base station 400 and the WT 500.

Relative user strength matching module 450 may use channel quality report information 480 received from multiple WTs to classify users as weaker/stronger relative to each other and match users, e.g., one relatively weaker versus one relatively stronger, for parallel scheduling on a given channel segment. In some embodiments, the relative strength matching routine 450 may use other criteria in addition to or in place of the channel quality report information 480 to determine WT matching. For example, some WTs in a wireless terminal constellation, e.g., low cost devices, may not have adequate demodulation and/or decoding capabilities to decode weak signals superimposed with strong signals and thus will not be arranged as strong receivers. Other WTs in the group, e.g., fixed wireless devices with less stringent specifications and power constraints, may be good candidates for decoding weak signals superimposed on strong signals, and thus may be good candidates to arrange as strong receivers.

WT power control routine 438 controls the transmit power levels of WTs operating within the cell of BS 400. Received power target module 452 uses data/information 430 including received power target model information 499, coding information 492, and relative strength indication information 494 to determine a received power target for uplink signals in the uplink portion. The transmit power control routine 440 uses the data/information 430, including the transmit power model information 498, the coding information 492, and the relative strength indicator information 494, to control the transmitter 406 to transmit downlink signals at the appropriate assigned strength for a given segment. Signaling routines 442 may be used by the receiver 402, transmitter 406, and I/O interface 412 to control the generation, modulation, encoding, transmission, reception, demodulation, and/or decoding of communicated signals.

Fig. 5 is an illustration of an exemplary wireless terminal 500 implemented in accordance with the present invention. Exemplary wireless terminal 500 may be a more detailed illustration of any of terminal nodes 310, 312, 318, 320 of fig. 3. The wireless terminal 500 may be a fixed or mobile wireless terminal. Mobile wireless terminals are sometimes referred to as mobile nodes and may move throughout the system. The wireless terminal 500 includes a receiver 502, a transmitter 504, a processor 506, and a memory 508 coupled together via a bus 510 over which the various elements can exchange data and information.

Receiver 502 is coupled to an antenna 511 through which wireless terminal 500 may receive downlink signals from base station 400. Such downlink signals may include controlled superposition assignment signals, controlled superposition downlink traffic signals, and/or controlled superposition acknowledgement signals transmitted by base station 400, in accordance with the present invention. The receiver 502 includes a plurality of demodulation modules, demodulation module 1512, and demodulation module N514. In some embodiments, the demodulation modules 512, 514 may be part of a decoder module. The demodulation modules 512, 514 are connected together. The demodulation module 1512 may perform a first demodulation on the received superimposed signal to recover a high power or well protected signal. The demodulation information may be forwarded from demodulation module 1512 to demodulation module N514. Demodulation module N514 may remove the high power or well protected signal from the received superimposed signal and then demodulate the low power or less protected signal. In some embodiments, a separate receiver 502 and/or separate antenna 511 may be used, e.g., a first receiver for high power or well protected downlink signal recovery and a second receiver for low power or less protected downlink signal recovery. In some embodiments, it is possible to directly decode weaker or less protected signal components in the superimposed downlink signal without first removing the effect of the stronger or better protected signal components.

Transmitter 504 is coupled to an antenna 515 through which wireless terminal 500 may transmit uplink signals to base station 400. Such uplink signals may include uplink traffic channel signals and acknowledgement signals. The transmitter 504 includes a modulation module 516. The modulation module 516 may modulate data/information into uplink signals. In some embodiments, the modulation module 516 may be part of an encoder module. The transmitter 504 may be controlled in accordance with the output power and/or modulation to output uplink signals having different target received power levels and/or different relative protection levels, e.g., a high target received power signal (or a well-protected signal) and a low target received power signal (or a less protected signal) for different uplink channel portions in accordance with the present invention.

Memory 508 includes routines 518 and data/information 520. Routines 518 include a communications routine 522 and wireless terminal control routines 524. Wireless terminal control routines 524 include signaling routines 526 and channel quality measurement module 528. Signaling routines 526 include a receiver control module 530 and a transmitter control module 532. The receiver control module 530 includes a plurality of signal detection modules, a first signal detection module 534 and an nth signal detection module 536. Transmitter control module 532 includes a signal generation module 538 and a transmitter power control module 539.

Data/information 520 includes data 540, terminal Identifier (ID) information 542, section information 544, mode information 546, channel quality information 548, tone information 550, modulation information 552, timing information 554, transmit power model information 556, received power target model information 558, received downlink assignment messages 560, received downlink traffic channel messages 562, acknowledgement messages for downlink traffic 564, uplink assignment messages 566, uplink traffic channel messages 568, and received acknowledgement messages for uplink traffic 570.

Data 540 includes user data, e.g., data from a communications peer of WT500 via BS400 and data received in downlink signals from BS 400. Data 540 also includes user data intended for peer nodes of WT500 (e.g., another WT in a communication session with WT 500) to be transmitted in uplink signals to BS 400. Terminal ID information 542 includes a base station assigned ID used to identify WT500 in communications and operations with BS 400.

Segment information 544 includes a plurality of communications channel segment information sets, segment 1 information 574, segment N information 576, corresponding to channel segments assigned to WT 500. Section 1 information 574 includes section type information 578, section Identifier (ID) information 580, coding information 582, and relative strength indication information 584. Section 1 information 574 includes section type information 578, section ID information 580, coding information 582, and relative strength indication information 584. Section type information 578 includes information identifying the type of the section, e.g., assignment section for uplink traffic, assignment section for downlink traffic, uplink traffic channel section, downlink traffic channel section, acknowledgment channel section corresponding to the uplink traffic channel section, acknowledgment section corresponding to the downlink traffic channel section. Portion identifier information 580 may include information identifying the portion, e.g., information identifying a frequency, time, duration, and/or specification associated with the portion. Coding information 582 includes information identifying the type of coding and/or modulation used for the portion. Relative strength designation information 584 includes information indicating the designated WT relative strength for the purposes of communication on the segment. In some embodiments, relative strength designation information 584 includes information identifying a WT as a weak or strong WT for purposes of communication on the segment.

Channel quality report information 548 includes downlink channel quality information such as SNR (signal to noise ratio), SIR (signal to interference ratio). Channel quality report information 548 may be obtained from measurements of downlink signals (e.g., measurements of pilot signals and/or beacon signals) received from BS 400. Channel quality report information 548 is fed back to BS400 and used by BS400 to decide on opportunistically matching and scheduling users as relatively weaker/stronger WTs on the same segment in accordance with the present invention.

Mode information 546 includes information indicating the current mode of WT 1, e.g., on state, sleep state, etc. Tone information 550 includes information identifying tones used in hopping sequences, channels, and/or segments. Modulation information 552 includes information used by WT500 to perform various modulation and/or coding schemes, e.g., coding rate information, modulation type information, error correction code information, etc. Timing information 554 may include timing information for the hopping sequence, parent slot, pause, duration of a channel segment, and timing relationships between different types of channel segments, such as between an assignment segment, a corresponding traffic channel segment, and a corresponding acknowledgement channel segment. Received power model target information 558 may include information such as a look-up table for specifying a model for controlling WT transmit power to transmit at an appropriate power level to achieve a received power target at BS400 for uplink channel segment signals. In some embodiments, the received power model target for wireless terminal 500 is a function of the code rate and the class of the user (wireless terminal) as a strong or weak user (wireless terminal). In such an embodiment, the received power target between the strong and weak classes may differ significantly, for example by a value of > 3dB, like 10dB, for the same code rate.

Received downlink assignment messages 560 include assignment messages received from BS400 notifying WT terminal 500 that it has been assigned a downlink traffic segment. Downlink assignment messages are transmitted by BS400 to WT500 on downlink assignment channel segments. Received downlink assignment messages 560 may be one of a plurality of downlink assignment messages transmitted to multiple WTs on the same assignment segment using controlled superposition coding, in accordance with the present invention. Received downlink traffic messages 562 include data and information, e.g., user data, transmitted from BS400 to WTs on downlink traffic channel segments. Received downlink traffic channel messages 562 may be one of a plurality of downlink traffic messages transmitted to multiple WTs on the same assignment segment using controlled superposition coding in accordance with the present invention. Downlink traffic acknowledgement messages 564 include acknowledgement messages to be transmitted by WT500 to BS400 indicating whether WT500 successfully received data/information on the assigned downlink traffic channel segment. Acknowledgement messages 564 may be transmitted by WT500 to BS400 at a controlled received power target on the same assignment segment used by other WTs in accordance with the invention.

Received uplink assignment messages 566 include assignment messages used to notify WT500 that it has been assigned an uplink traffic segment. Received uplink assignment messages 566 are obtained from received signals transmitted by BS400 to WT500 on downlink channel segments for assigning uplink channel segments. Received uplink assignment message 566 may be one of a plurality of uplink assignment messages transmitted by BS400 to a plurality of WTs on the same assignment segment as part of a controlled superposition signal in accordance with the invention. Uplink traffic channel messages 568 include data and information, e.g., user data, transmitted from WT500 to BS400 on uplink traffic channel segments. Uplink traffic channel messages 568 may be transmitted by WT500 to BS400 at a controlled received power target on the same allocated portion as other WTs transmitting uplink traffic channel messages, and signals from multiple WTs may be superimposed in the air link, in accordance with the present invention. Acknowledgement messages for uplink traffic 570 include acknowledgement signals from BS400 to WTs indicating whether or not BS400 successfully received data/information on the assigned uplink traffic channel segment. In accordance with the invention, base station 400 may transmit multiple acknowledgement messages to multiple WTs on the acknowledgement segment in a combined controlled superposition signal.

Communications routine 522 is used to control wireless terminal 500 to perform various communications operations and implement various communications protocols. Wireless terminal control routines 524 are used to control the operation of the wireless terminal 500, such as the receiver 502 control, the transmitter 504 control and to perform the steps of the method of the present invention. Signaling routines 526 include a receiver control module 530 for controlling the associated downlink signaling and a transmitter control module 532 for controlling the associated uplink signaling. The receiver control module 530 directs the operation of the receiver 502 to receive, demodulate and/or decode the downlink signals including the superimposed signals from the base station 400. The first signal detection module 534 uses the data/information 520 including the modulation information 552 and the portion information 544 to control the demodulation module 1512 to receive and process signals, such as to recover high power or well-protected signals from a superimposed downlink signal. The nth signal detection module 536 uses the data/information 520 including the modulation information 552 and the partial information 544 to receive and process signals, such as to recover low power or less protected signals from a superimposed downlink signal. The transmitter control module 532 directs the operation of the transmitter 504 and its modulation module 516 for operations related to uplink signaling such as signal generation and power control. Signal generation module 538 uses data/information 520 including modulation information 552 and partial information 544 to generate an uplink signal, e.g., uplink traffic channel message 568, from the uplink information to be communicated. Transmitter power control module 539 uses data/information 520 including received power target model information 558 and segment information 544, e.g., coding information 582 and relative strength designation information 584, to control the transmitter to adjust the uplink signal strength of the uplink segments, e.g., individual uplink segments. In accordance with the invention, the transmitter power control module 539 may adjust the transmit power level of the various segments in an attempt to achieve a target level of received power at the base station 400. Control of wireless terminal transmit power relative to the expected receive power at the base station allows the base station 400 to opportunistically arrange multiple wireless terminals on the same uplink portion with different receive power targets to receive uplink signals including superimposed signals from the multiple wireless terminals and extract independent signals from each wireless terminal.

Channel quality measurement module 528 performs measurements of received signals (e.g., pilot signals and/or beacon signals) to obtain channel quality information 548.

Exemplary embodiments of the present invention are described below in the context of a cellular wireless data communication system. The exemplary system is similar to the systems disclosed in U.S. patent applications 09/706,377 and 09/706,132, which are incorporated by reference herein, but include modifications for practicing the invention. Although a typical wireless system is used for the purpose of explaining the invention, the scope of the invention is broader than the examples and, in general, is equally applicable to many other communication systems.

In a wireless data communication system, air link resources typically include bandwidth, time, and/or code. The air link resources that transport data and/or voice traffic are referred to as traffic channels. Data is communicated over a traffic channel in a traffic channel segment (traffic segment for short). The traffic segment may be a basic or minimal unit of available traffic channel resources. The downlink traffic segment transmits data traffic from the base station to the wireless terminals, and the uplink traffic segment transmits data traffic from the wireless terminals to the base station. One typical system in which the present invention is used is a spread spectrum OFDM (orthogonal frequency division multiplexing) multiple access system in which the traffic segment includes a number of frequency tones within a finite time interval.

In a typical system for explaining the present invention, traffic segments are dynamically shared between wireless terminals communicating with a base station. Scheduling functionality, such as a module in a base station, may assign each uplink and downlink portion to one or more wireless terminals, such as mobile terminals, based on a number of criteria.

Different users may be assigned traffic segments from one segment to another. Fig. 6 is a diagram 600 of frequency on vertical axis 602 versus time on horizontal axis 604 and represents a typical traffic segment. Traffic segment a 606 is represented by a rectangle with vertical line shading, while traffic segment B608 is represented by a rectangle with horizontal line shading. In the example of fig. 6, traffic segments a 606 and B608 occupy the same frequency but occupy different time periods. In fig. 6, it is assumed that a part a 606 is allocated to a user #1 and a part B608 is allocated to a user #2 by a scheduler of the base station. The base station's scheduler may quickly assign traffic channel segments to different users according to their traffic needs and channel conditions, which may typically vary over time. In this way, traffic channels are effectively shared and dynamically allocated between different users on a portion-by-portion basis.

In a typical system, assignment information for traffic channel segments is transmitted in an assignment channel that includes a series of assignment segments. In a cellular radio system, the allocation portion is typically transmitted in the downlink. There is an assignment segment for the downlink traffic segment and a separate assignment segment for the uplink traffic segment. Each traffic segment may be, and typically is, associated with a unique assignment segment. The associated assignment segment conveys assignment information for the corresponding traffic segment. The allocation information may include an identifier of the user terminal allocated to use the traffic segment, the coding and/or modulation scheme used in the traffic segment. For example, fig. 7 is a diagram 700 illustrating exemplary assignment and traffic segments. Fig. 7 shows frequency on the vertical axis 702 versus time on the horizontal axis 704. Fig. 7 includes two assignment segments, a '706 and B' 708, and two traffic segments, traffic segment a 710 and traffic segment B712. The exemplary allocation portions 706, 708 occupy the same frequency but occupy different time periods. The exemplary traffic segments 710, 712 occupy the same frequency but occupy different time periods. The assignment segments 706, 708 occupy different frequencies than the traffic segments 710, 712. Assignment segment a' 706 conveys the assignment information for traffic segment a 710 as indicated by arrow 714. Assignment segment B' 708 conveys the assignment information for traffic segment B712 as indicated by arrow 716. Each assignment segment 706, 708 precedes its respective traffic segment 710, 712. The allocation channel is a shared channel resource. The user receives the assignment information conveyed in the assignment channel and then uses the traffic channel segment in accordance with the assignment information.

Data transmitted by the base station on the downlink traffic segment is decoded by a receiver in the intended wireless terminal, while data transmitted by the assigned wireless terminal on the uplink segment is decoded by a receiver in the base station. Typically, the transmitted portion includes redundant bits to assist the receiver in determining whether the data was decoded correctly. This is required because the wireless channel may be unreliable and useful data traffic typically has a high integrity requirement.

The transmission of the traffic segment may succeed or fail due to interference, noise and/or channel fading in the wireless system. In a typical system, the receiver of a traffic segment sends an acknowledgement to indicate whether the segment was received correctly. Acknowledgement information corresponding to a traffic channel segment is transmitted in an acknowledgement channel comprising a series of acknowledgement segments. Each traffic segment is associated with a unique acknowledgement segment. For the downlink traffic segment, the acknowledgement segment is in the uplink. For the uplink traffic segment, the acknowledgement segment is located in the downlink. The acknowledgement segment may convey at least one bit of information, e.g., a bit, to indicate whether the associated traffic segment was received correctly. Due to the predetermined association between the uplink traffic segment and the acknowledgement segment, there may be no need to communicate other information in the acknowledgement segment, such as a user identifier or a segment index. The acknowledgement segment is typically used by the user terminal using the associated traffic segment and not by other user terminals. Thus, in both uplink and downlink, the acknowledgment channel is a shared resource because it can be used by multiple users. However, there is typically no contention problem caused by the use of the common acknowledgement channel, since there is typically no ambiguity that the user terminal will use a particular acknowledgement segment. Fig. 8 includes a diagram 800 illustrating an exemplary downlink traffic channel portion and a graph 850 illustrating an exemplary uplink acknowledgement portion. Diagram 800 depicts frequency on vertical axis 802 versus time on horizontal axis 804. Diagram 800 includes a downlink traffic segment a 806 indicated by vertical line shading and a downlink traffic segment B indicated by horizontal line shading. Each traffic segment 806, 808 occupies the same frequency but a different time slot. Graph 850 plots frequency on vertical axis 852 versus time on horizontal axis 854. Graph 850 includes uplink acknowledgement segment A "856 and uplink acknowledgement segment B" 858. Each acknowledgement segment 856, 858 occupies the same frequency but a different time slot. The two uplink acknowledgement segments, a "856 and B" 858, convey the acknowledgement information for downlink traffic segments a 806 and B808, respectively. The link between traffic segment A806 to acknowledgment segment A' 856 is represented by arrow 860; the link between the traffic part B808 and the acknowledgement part B "858 is indicated by an arrow 862.

The present invention achieves the benefits of superposition coding in a multi-user communication system while using a simple receiver design in both the broadcast channel and the multiple access channel. The advantage of using superposition coding is even greater in systems where the channel quality experienced by different users has a large dynamic range. In wireless communication systems, it is common to find channel quality variations of up to 30dB or even higher (three orders of magnitude) between individual users. The advantages brought by the present invention significantly affect the increased system capacity in such systems.

Superposition coding in the context of a downlink (broadcast) channel in accordance with the present invention will now be described. Consider a downlink (broadcast) channel in a multi-user wireless communication system such as that just described. The transmitter of the downlink (broadcast) channel is a base station and the receivers are mobile or fixed wireless user terminals (e.g., sometimes referred to as mobile users or subscribers) served by the base station. An example of such a system is shown in exemplary system 900 of fig. 9, where base station 902 communicates on the downlink and uplink via wireless links 912, 914, 916, 918 to four mobile users, mobile user 1904, mobile user 2906, mobile user 3908, and mobile user 4910, respectively. Mobile users 904, 906, 908, 910 are at different distances from base station 902 and may therefore experience different channel conditions. Users 904, 906, 908, 910 frequently update base station 902 with measurements of the downlink channel quality and interference conditions they are currently experiencing. Base station 902 typically uses this information to schedule users for transmission and to assign downlink channel resources to them. For example, base station 902 can use channel quality and interference condition reports to allocate transmit power to different users 904, 906, 908, 910 on a broadcast channel. Users, such as mobile user 2906 and mobile user 4910, that are closer to base station 902 are typically allocated less power, while users, such as mobile user 1904 and mobile user 3908, that are located farther from base station 902 are allocated more power. The bandwidth may be appropriately allocated to the different users 904, 906, 908, 910 depending on the channel conditions. The most commonly used measure of channel quality is the received signal-to-noise ratio (SNR), but other similar or comparable measures may be used.

In accordance with the invention, the base station scheduler may choose to arrange two or more user terminals on the same traffic segment. The selected terminal should preferably have an SNR that spans a wide dynamic range. Superposition coding is used to transmit data to selected terminals on the same traffic segment. It should be noted here that in practice, while the advantage of using superposition coding is achievable by arranging two suitably selected users on a given traffic segment, in some embodiments, more users may be arranged. Arranging a small number of users, e.g. two, has the advantage of causing a significantly reduced decoding effort at the user terminals compared to the case where more users (> 2) are arranged on the same traffic segment.

In accordance with the present invention, the base station is not always required to use superposition coding, but may do so in an opportunistic manner. When it is not feasible or practical to schedule users experiencing different channels, the base station may default to a simple state where it transmits to a single user.

In this regard, one important feature that should be emphasized is that the user does not need, and is not generally pre-assigned, the "strong" and "weak" labels. The classification of users into "weaker" and "stronger" subsets is not a static distinction, but rather a relative definition of users that may be simultaneously scheduled in the same broadcast channel. For example, consider three users, denoted as "a", "B", "C", labeled in descending order of channel quality, i.e., user "a" has the best channel quality, user "C" has the worst channel quality, and user "B" has a medium channel quality. In the case of a broadcast channel, when two users, "B", "C", are transmitted together using superposition coding, the transmitter will consider "B" as a "strong user" and "C" as a "weak user". On the other hand, when transmitting to users "a" and "B" at the same time, user "a" is considered as a strong user, and user "B" is considered as a weak user. In the case of a broadcast channel, users may derive their current status from a control channel that transmits allocation information as to which user is currently scheduled to use a high or low power signal. In general, signals intended for weaker users are more protected, e.g., using better coding or higher power, than less protected signals intended for stronger users.

Superposition coding in the context of an uplink (multiple access) channel in accordance with the present invention will now be described. An important aspect of the present invention is that it can be applied in dual sensing in a multiple access environment. The receiver of the uplink (multiple access) channel is the base station and the transmitter is the user terminal served by the base station. Typically, multiple access channels are allocated in time or code space or frequency between users. Alternatively, the channel may be shared among multiple users, whose signals interfere with each other at the base station receiver. A CDMA system is an example of a system in which a channel may be shared among multiple users. Joint detection (also known as multi-user detection) techniques may be used to separate the user signals. In practice, however, this is quite complicated. In accordance with the present invention, a base station scheduler may select two or more user terminals to transmit uplink data on the same traffic segment resources. The signal from the selected terminal is superimposed in the transmission medium. Fig. 10 is a diagram 1000 illustrating superposition coding in a multiple access channel in accordance with the present invention. FIG. 10 shows the difference of two superimposed signalsA power target is received. Figure 10 includes an exemplary high power QPSK signal represented by four shaded circles 1002 shown and an exemplary low power QPSK signal represented by four unshaded circles 1004. The strength of the high power signal may be scaled from the origin 1008 to the point 1002Is represented by the long arrow 1006, while the strength of the low power signal may be represented by the magnitude from the origin 1008 to the point 1004Indicated by short arrows 1010. The base station scheduler may operate in coordination to receive selected user terminal uplink signals at different power levels. In one embodiment, wireless terminals with smaller path losses may be operated so that their uplink signals will be received by the base station at a relatively higher power, while wireless terminals with larger path losses may be operated so that their uplink signals will be received by the base station at a relatively lower power. In this case, it would be advantageous for the scheduler to select user terminals that span a large range of path loss for the same traffic segment. In another embodiment, suitable for use in a cellular system, user terminals causing less off-cell interference may be operated so that their signals will be received by the base station at a relatively higher power, while user terminals causing more off-cell interference may be operated so that their signals will be received by the base station at a relatively lower power. In this case, the scheduler may select terminals that span a large (their generated) out-of-cell interference range for the same traffic segment.

It should also be noted that in practical systems, by operating the scheduler to select two user terminals to transmit on the same traffic segment, most of the gain in superposition coding usage is available. The described embodiment of arranging superposition coding of two users on the same traffic segment has the advantage of making the base station receiver simple, as opposed to arranging three or more users on the same traffic segment.

The user is not pre-assigned "strong" and "weak" labels. In accordance with the present invention, a user is marked as "stronger" or "weaker" in a relative context. In this case, a "strong" user refers to a user terminal that is operated to receive at a higher power than another "weaker" user transmitting on the same traffic segment. The user may know whether it should target a higher or lower received power level (e.g., from a control channel), where the base station may, and in various embodiments does, indicate the user's allocation information for the traffic channel.

In case the base station is constrained, it may choose not to schedule more than one user terminal on one traffic segment. This option is completely transparent to the user, who does not need to do anything different, whether or not overlay is used.

The use of superposition coding on the allocation channel in accordance with the present invention will now be described. A typical application of the present invention to allocating channels will now be described in detail in this section using the context of a typical OFDM-based cellular radio system.

In a typical system, a downlink traffic channel is suitable for the field of broadcast communication methods, and an uplink traffic channel is a typical example of a multiple access communication method. Both downlink and uplink traffic segments are dynamically allocated to users in accordance with the scheduler decisions made by the base station scheduler. Moreover, the base station scheduler also determines the coding and modulation rates for the traffic segments. An assignment channel is a control channel that conveys assignment information to wireless terminals, e.g., mobile user terminals. This embodiment of the invention is described using two subsystems, one for the downlink broadcast channel and the other for the uplink multiple access channel.

The subsystem of the downlink broadcast channel will be described first. Each mobile user in the system updates its downlink channel state frequently to the base station, e.g., in channel quality and interference condition feedback reports. The report may include various parameters such as signal-to-noise ratio, channel frequency profile, fading parameters, and the like. The base station schedules two or more users and superimposes user signals on each downlink traffic segment. The base station also selects parameters for the superimposed signal, such as coding rate and transmit power. The scheduler's decision on the traffic segment is communicated in the corresponding allocation segment, which is monitored by the user, e.g., the wireless terminal. When multiple users are arranged on the same data portion in the context of the described embodiment of the invention, the allocation information may also be superposition coded on the allocation portion.

To emphasize this feature of the present invention, consider an example in which two users are assigned the same traffic segment 1108, as shown in diagram 1100 of FIG. 11. Fig. 11 includes two exemplary receivers, a weaker receiver 1102 and a stronger receiver 1104. Fig. 11 also includes an assignment segment 1106 and a traffic segment 1108. The base station transmits the combined assignment signal using superposition coding 1110 to both receivers 1102, 1104. The base station then transmits the traffic signal synthesized using superposition coding 1112 to both receivers 1102, 1104. The assignment information for the weaker receiver 1102 is transmitted as a superposition coded high power signal on the assignment channel and the assignment information for the stronger receiver 1104 is transmitted as a superposition coded low power signal on the assignment channel. The users 1102, 1104 first decode the high power signal component of the distribution portion 1106. If the user is assigned by the high power signal of assignment segment 1106, as with user 1102, the user knows that it is scheduled as a "weaker receiver" and should also decode the high power signal corresponding to composite signal 1112 of traffic channel segment 1108. Otherwise, the user should continue to decode the low power signal of the assignment segment 1106 because it may be considered a stronger receiver. Furthermore, if the user is assigned by the low power signal of the assignment segment, as with receiver 1104, then the user knows that it is scheduled as a "stronger receiver" and should continue decoding the low power signal of the corresponding traffic channel segment 1108. If the user is not assigned by the low power signal of assignment segment 1106, or even unable to decode the low power signal of composite assignment signal 1110, the user may be unable to decode the low power signal of composite traffic signal 1112 of traffic segment 1108 and choose not to attempt to decode it. In a more general case, a signal referred to as high power may be a better protected signal and a signal referred to as low power may be a less protected signal.

The controlled superposition coding paradigm described in the framework of the downlink subsystem can also be applied in the subsystem of the uplink multiple access channel. Fig. 12 is a diagram 1200 illustrating superposition coding used in broadcast assignment and multiple access traffic channels. Fig. 12 includes a legend 1201 indicating that the thick solid arrows represent downlink signals and the thick dashed arrows represent uplink signals. Fig. 12 includes a base station receiver 1202, a first user, e.g., a wireless terminal, designated as a weaker transmitter 1204, and a second user, e.g., a wireless terminal, designated as a stronger transmitter 1206. Fig. 12 also shows an allocation section 1208. A downlink composite assignment signal 1210 comprising superposition coding is transmitted from the base station to both wireless terminals 1204, 1206 over an assignment segment 1208. Wireless terminal 1204 transmits a signal 1212 including weaker user data 1214 to base station receiver 1202, while wireless terminal 1206 transmits a signal 1216 including stronger user data 1218 to base station receiver 1202. On the same uplink traffic segment, signals 1212 and 1216 are transmitted and the signals are superimposed over the air.

In particular, as shown in fig. 12, the base station schedules one or more users 1204, 1206, which later superimpose their signals 1212, 1216 on a single uplink traffic segment over the air. The base station may also select parameters, such as code rate and transmit power, for the superimposed signals 1212, 1216. The base station makes scheduling decisions to receive them at different powers at the base station, using a bias towards users whose power is in a sense controllable. For example, in accordance with the present invention, superimposed users may be users experiencing different path loss in the uplink, in one embodiment, or users having considerably different uplink out-of-cell interference effects, in another embodiment. The base station then communicates the decision using superposition coding in the downlink composite assignment signal 1210 on the assignment channel. A user, e.g., a mobile wireless terminal, first decodes the high power (better protected) signal of the assignment segment 1208. In one embodiment, if the user is assigned by the high power signal of assignment segment 1208, the user concludes that it is scheduled by the base station as a "weaker transmitter" and should transmit on the corresponding uplink traffic segment to be received at a lower power. In fig. 12, the user 1204 concludes that it is scheduled by the base station as a weaker transmitter and transmits the uplink traffic signal 1212 at a low target received power level. Similarly, if the user is able to decode the low power (less protected) signal included in the composite signal 1212 on the assignment channel 1208 and finds that this is scheduled, it infers that its current state is "stronger transmitter". It then continues transmitting at the appropriate transmit power on the corresponding uplink traffic segment so that it is received at a higher power. In fig. 12, user 1206 first decodes and removes the weaker user assignment and then decodes the stronger user assignment, finds that this is scheduled, infers that it is the stronger transmitter, and transmits uplink traffic signal 1216 at a high target received power level. If a user is not assigned by the low power signal of the assignment segment, or is not even able to decode the signal, the user may not use the corresponding uplink traffic segment with a "strong transmitter". In other embodiments, the concept of stronger and weaker transmitters may be defined in accordance with other criteria, such as uplink interference cost or device-related constraints.

Superposition coding, in accordance with the present invention, can be, and is, performed in an opportunistic manner and need not be performed on every traffic segment. This allows for significant flexibility in the base station scheduler. In the presence of both downlink and uplink subsystems, in some embodiments, low power signals are transmitted on the assignment channel when a user is found to have different channel states, and at other times, no low power signals are transmitted on the assignment channel. Otherwise, if the high and low power signals are all transmitted on the same channel segment when different channel conditions do not exist, the user may be able to detect the high power signal on the assignment channel, but may decode noise when they attempt to decode a possibly superimposed low power signal.

The use of superposition coding on the acknowledgment channel will now be discussed. In a typical OFDM-based system, after receiving the traffic segment, the receiver typically sends an acknowledgement in an acknowledgement channel to inform the transmitter whether the traffic segment has been correctly received. In particular, in some embodiments, for each downlink traffic segment there is a corresponding uplink acknowledgement segment, and for each uplink traffic segment there is a corresponding downlink acknowledgement segment.

If the downlink traffic segment is allocated to more than one user using superposition coding, then each of those allocated users should send an acknowledgement. In accordance with some embodiments of the present invention, the uplink acknowledgement channel is implemented as a multiple access channel using a multiple access communication method. From the framework of controlled superposition coding as described above in the case of using the multiple access communication method, the users superpose their acknowledgements on the same acknowledgement segment. The diagram 1300 of fig. 13 is used to represent superposition coding used in broadcast services and superposition coding used in multiple access acknowledgment channels. Fig. 13 includes a legend 1301 indicating that the heavy solid arrows represent downlink signals and the heavy dashed arrows represent uplink signals. Fig. 13 includes a base station receiver 1302, a first user 1304, e.g., a wireless terminal, designated as a weaker receiver/transmitter, and a second user 1306, e.g., a wireless terminal, designated as a stronger receiver/transmitter. Fig. 13 also includes a downlink traffic segment 1308 and a composite downlink signal 1310 that uses superposition coding. A downlink composite traffic signal 1310 is transmitted from the base station to both users 1304, 1306 on the same downlink traffic segment 1308. Fig. 13 also includes an uplink acknowledgement signal 1312 from user 1304 to base station receiver 1302 and an uplink acknowledgement signal 1314 from user 1306 to base station receiver 1302. Signal 1312 is transmitted at a low target received power and signal 1314 is transmitted at a high target received power. The uplink acknowledgement signals 1312 and 1314 are transmitted and superimposed over the air on the same acknowledgement segment 1316.

Fig. 13 shows two users 1304, 1306 receiving their superposition coded downlink traffic segments 1308. The two users 1304, 1306 then transmit their acknowledgments 1312, 1314 on the same acknowledgment segment 1316 at different target received power levels. In one embodiment of the invention, the user of the receiver (receiving less protected information) identified as stronger for the traffic segment is automatically considered as the stronger transmitter for the acknowledgment segment, targeting higher received power to send its acknowledgment. In fig. 13, user 1306 is identified as the stronger receiver of traffic segment 1308 and is considered the stronger transmitter. User 1306 first decodes and removes the better protected signal for weaker user 1304 and then decodes the data intended for user 1306. At the same time, the user of the weaker receiver identified as the traffic segment is automatically considered the weaker transmitter of the acknowledgment segment, targeting a lower received power to send its acknowledgment. In fig. 13, user 1304 is identified as the weaker receiver of traffic segment 1308 and is considered the weaker transmitter.

If superposition coding is used to allocate an uplink traffic segment to more than one user, the base station needs to send acknowledgements to multiple users. In accordance with the present invention, the downlink acknowledgment channel is considered to be a broadcast channel. From the above framework of controlled superposition coding in a broadcast channel, the base station superposes acknowledgements on the same acknowledgement segment. Fig. 14 shows an exemplary superposition coding for use in a multiple access traffic channel and an exemplary superposition coding for use in a broadcast acknowledgment channel. Fig. 14 includes a diagram 1401 illustrating that thick solid arrows represent downlink signals and thick dashed arrows represent uplink signals. The diagram 1400 of fig. 14 includes a base station receiver/transmitter 1402, a first user 1404, e.g., a wireless terminal, designated as a weaker transmitter/receiver, and a second user 1406, e.g., a wireless terminal, designated as a stronger transmitter/receiver. User 1404 transmits its uplink traffic signal 1408 at a low target received power, while user 1406 transmits its uplink traffic signal 1410 at a high target received power. Fig. 14 shows two users 1404, 1406 transmitting their uplink traffic signals 1408, 1410 on the same traffic segment 1412 and superimposing the two signals over the air. The base station 1402 then sends two acknowledgements in the combined downlink acknowledgement signal 1416 on the same acknowledgement segment 1414 at different transmit power levels for each acknowledgement. In one embodiment of the invention, the user identified as the stronger transmitter of the traffic segment 1412 is automatically considered the stronger receiver of the acknowledgment segment 1414, so that the base station sends its acknowledgment at a low transmit power (less protected). In fig. 14, user 1406 is identified as the stronger transmitter so that the base station transmits an acknowledgement signal for user 1406 at a low transmit power. User 1406 receives signal 1416 and first decodes and removes the better protected signal for the weaker user 1404 and then decodes its own acknowledgement signal. At the same time, the user identified as the weaker transmitter of the traffic segment 1408 is automatically considered the weaker receiver of the acknowledgment segment 1414, so that the base station 1402 sends its acknowledgment at a high transmit power (better protected). In fig. 14, user 1404 is identified as a weaker transmitter, so that base station 1402 sends the acknowledgement signal of user 1404 at a high transmit power.

An embodiment of the present invention using an overlaid common control channel will now be described. In some embodiments of the present invention, controlled superposition coding is used to reduce the transmit power level on a common control channel used in a multi-user communication system. Common control channels are often used to transmit control information to each user in the system. Therefore, they are usually transmitted at high transmit power in order to reach the worst case user. The embodiments will be described in the context of a cellular wireless communication system, but may be more generally applicable. The exemplary embodiment assumes a common control channel that is transmitted by the base station on the downlink and monitored by the wireless end users (e.g., each mobile user in a cell). According to the present invention, the control information is divided into two groups. The first group is referred to as "regular information" intended for the mainstream user. The mainstream user groups are those mobile users that have the appropriate downlink channel conditions, e.g., the appropriate downlink SNR. The second group is called "protected information" which is intended to be received by most or all mobile users in the system, i.e. not only the primary users but also the weaker users with poor downlink SNR. According to the invention, the protected control information is transmitted at a high power per bit, which enables it to be received well by some or all weak users in the system. Then, on the protected information, the regular information is superimposed at the rated power per bit. The weak user may not be able to decode the full information but should be able to decode the protected information from the superimposed signal, whereas the mainstream user will be able to decode both the protected and the regular information.

One application of this embodiment is shown in fig. 15. Fig. 15 is a diagram 1500 illustrating the application of superposition coding to a common control channel. Fig. 15 includes a first user 1502, e.g., a wireless terminal, designated as the weaker receiver and a second user 1504, e.g., a wireless terminal, designated as the stronger receiver. Fig. 15 also includes an assignment segment 1506, a composite assignment signal 1512 using superposition coding, a downlink traffic segment "a" 1508, and a downlink traffic segment "B" 1510. Downlink traffic segment "a" is intended for the weaker receiver 1502 and downlink traffic segment "B" is intended for the stronger receiver 1504.

As depicted, there are two traffic segments, a 1508 and B1510. In the single allocation portion 1506, the allocation information for those two traffic portions is transmitted using superposition coding. In particular, the allocation information of part a is considered as protected information and the allocation information of part B is considered as regular information. The primary stream user, e.g., user 1504, can decode both allocations and thus can be arranged in either of traffic segments 1508, 1510. In this example, the stronger receiver 1504 first decodes and removes the better protected signal for the weaker receiver 1502 and then decodes its allocation. While weak users, e.g., 1502, on the other hand, can only decode the assignment of part a 1508 and thus can only be scheduled in part a 1508. It is important to note that in this example, the superposition coding on the assignment channel does not necessarily depend on the superposition coding on the corresponding traffic segment. Traffic segment "a" and traffic segment "B" are different traffic segments, and signals 1514 and 1516 are different signals and are not superimposed. Superposition coding on the common control channel is a valuable practical technique in its own right and may lead to power savings and increased robustness.

Fig. 16 is a diagram 1600 of an exemplary uplink signal included on the same uplink channel segment and is used to illustrate the concept of a target received power in accordance with one embodiment of the present invention. Figure 16 includes two exemplary wireless terminals WT 11602, WT 21604 implemented in accordance with the present invention and one exemplary base station 1606 implemented in accordance with the present invention. The channel gain between WT 11602 and BS 1606 is G₁1610 and known to both WT 11602 and BS 1606, e.g., by measurements of pilot signals and feedback channel quality reports. The channel gain between WT 21604 and BS 1606 is G₂1612 and known to both BS 1606 and WT 21604, e.g., by measurements of pilot signals and feedback channel quality reports. It is assumed that both WT 11602 and WT 21604 are transmitted using the same data rate, modulation, coding scheme, and coding rate. WT 11602 is designated by base station 1606 as the stronger transmitter of uplink channel segment 1608, and WT 21604 is designated by base station 1606 as the weaker transmitter of uplink channel segment 1608.

WT 11602 transmits uplink signal 1614 to BS 1606. Uplink signal 1614 includes power rating signal S with WT 1 uplink information₁And from the transmission gain value a₁To measure. From WT 11602 with a₁S₁A transmit signal 1614; however, due to channel loss, the signal received by the receiver of the base station is a₁G₁S₁(reduced level). As previously noted, WT 11602 knows G₁The channel value of (2). WT 11602 preconditions a₁To reach a value of₁G₁Indicated high received power target.

The channel gain between WT 21604 and BS 1606 is G₂1612 and known to both BS 1606 and WT 21604, e.g., by measurements of pilot signals and feedback channel quality reports. WT 21604 transmits uplink signal 1616 to BS 1606. Uplink signal 1616 includes power rating signal S with WT 2 uplink information₂And from the transmission gain value a₂To measure. Signal 1616 at a₂S₂Leave the WT; however, due to channel loss, the signal received by the receiver of the base station is a₂G₂S₂(reduced level). As previously noted, WT 21604 knows G₂The channel value of (2). WT 2 Pre-adjust a₂To reach a value of₂G₂Indicated low received power target. Since the two signals 1614 and 1616 are transmitted on the same uplink channel portion 1608, the signals are superimposed over the air and are used by the base station 1606 as a composite signal (a)₁G₁)S₁+(a₂G₂)S₂1618 to receive.

Selecting two received power targets to match a₂G₂Low power target ratio, represented by a₁G₁The high power target represented is larger, e.g., much larger. By achieving different power target levels at BS 1606, the BS can distinguish between two signals from two independent devices (WT 11602, WT 21604) and separate from signal S₁And S₂To extract the information. Note that according to the channel gain, a₁May be less than a₂。

Fig. 17 is a flow chart 1700 of an exemplary method of operating a Base Station (BS) in accordance with the present invention. The exemplary method of flowchart 1700 uses controlled superposition in accordance with the present invention. In step 1702, base station operations are initiated, such as powering on and initializing the base station. Operation proceeds from step 1702 to step 1704. In step 1704, the BS monitors to receive a signal, e.g., an uplink signal from the WT. Operation proceeds from step 1704 to steps 1706 and 1722.

In step 1706, the BS receives channel quality reports from the multiple WTs. In step 1708, the BS stores a set of channel state information indicating the channel quality of each of the plurality of WTs. The set of stored channel state information includes, for example, individual channel signal-to-noise ratio information for each of the plurality of WTs. Operation proceeds from step 1708 to step 1710. In step 1710, the BS examines the set of channel state information to identify WTs whose channel states differ from each other by at least a pre-selected minimum value (e.g., 3dB or 5dB or 10 dB). Then, in step 1712, the BS determines whether there are at least two WTs identified as having channel conditions that differ by at least a preselected minimum value, which have signals to be transmitted in the communications channel segment available for assignment.

Operation proceeds from step 1712 to step 1714 if it is determined that at least two WTs identified as having channel conditions that differ by at least a preselected minimum value have signals to be transmitted in available channel segments. In step 1714, the BS assigns a communications channel segment for conveying superimposed signals corresponding to at least two different WTs identified as having channel conditions that differ by at least a preselected minimum value, e.g., a first WT having a better channel quality (at least exceeding the preselected minimum value) than a second WT. The assigned traffic channel segment may be, for example, a downlink channel segment, which is an assignment channel segment used to convey uplink traffic channel segment assignments (e.g., uplink traffic channel segment assignments) to WTs.

Operation proceeds from step 1714 to step 1716. In step 1716, the base station transmits a superimposed signal to two different identified WTs, the first WT and the second WT, in, for example, an assignment channel segment corresponding to the communication channel segment being assigned, said superimposed signal including a low power signal segment intended for said first WT and a high power signal segment intended for said second wireless terminal, said BS transmitting lower power signal segments at lower power than said high power signal segments. Operation proceeds from step 1716 to step 1704 where the base station monitors for additional signals.

If, in step 1712, it is determined that there are not at least two WTs having signals to be transmitted in the communications channel segment available for assignment and identified as having channel conditions that differ by at least a preselected minimum value, then operation proceeds to step 1718. In step 1718, the BS assigns an available traffic channel segment to a single one of the WTs. Operation proceeds from step 1718 to step 1720. In step 1720, the base station transmits an assignment signal to the single WT. Operation proceeds from step 1720 to step 1704, where the BS continues to monitor the signal.

From step 1704, operation also proceeds to step 1722. In step 1722, the base station receives a superimposed signal from the first and second WTs, the superimposed signal including first and second signal portions transmitted by the first and second WTs, respectively, the first signal portion being received by the BS at a higher power level than the second signal portion. Operation proceeds from step 1722 to step 1724. In step 1724, the BS decodes the first signal portion; removing a first signal portion from the superimposed signal; the second signal portion is then decoded. Operation proceeds from step 1724 to step 1704 where the base station continues to monitor to receive signals.

Figure 18 shows steps performed by a WT in accordance with an exemplary embodiment of the present invention in which superimposed uplink channel assignment messages are used to assign uplink traffic channel segments to the WT. Assignment messages intended for a particular WT include the particular terminal identifier of the WT. Assignment messages (e.g., terminal IDs) are transmitted to WTs with better channel conditions on the low power portion of the superimposed assignment message signal, while WTs with worse channel conditions are assigned on the high power portion of the superimposed assignment message signal.

The method 1800 begins at start step 1802. Next, in step 1804 the WT is initialized, e.g., as part of a power-on operation. Once in the active state, the WT periodically measures the channel state and reports the channel state to the interacting BSs in step 1806. In step 1808, the WT periodically receives transmit power control adjustment information from the BS. From this information, the WT can predict what the received power at the BS will be for a particular transmit power level. Thus, the BS power control information allows the WT to determine the required transmit power level to meet the target received power level. The WT maintains information, e.g., a table including different gain factors, which may be used to achieve different received power levels, which may be used in conjunction with WT feedback information indicating the transmit power required to achieve a particular reference level. When used to adjust the transmit power level in conjunction with the receive power control feedback information, the gain factor may be used as a bias to the gain required to reach a particular reference level, resulting in a receive power level associated with the gain factor.

Monitoring the channel assignment message occurs in step 1810. Steps 1806, 1808 and 1810 are performed onward while the WT remains active. For each assignment message received in step 1810, operation proceeds to step 1812. In step 1812, a superposition decoding operation is performed on the received assignment message, which is a superposed signal including a first signal portion and a second signal portion, the first and second signal portions being transmitted at different power levels, wherein the first signal portion is a higher power portion. Decoding step 1812 includes sub-step 1814 in which a first signal portion, e.g., a high power portion, is decoded. The first signal portion is then removed from the received assignment message in step 1816 to produce a second (low power) signal portion that is decoded in sub-step 1818. If the WT has poor channel conditions, it may only be able to decode the first (high power) signal portion, for which reason the BS uses the high power signal portion to convey assignment information to WTs having worse communication channels.

After completion of superposition decoding, operation proceeds to step 1820, where the decoding results are examined to determine which of the first and second signal portions is intended for the WT, e.g., the WT checks to determine which portion includes its particular WT identifier. Assuming that the WT to which the segment is being assigned has a better channel condition, the WT will detect its ID in the low power signal segment of the transmitted signal.

Operation proceeds from step 1820 to step 1824 via connection point a 1822. In step 1824, the WT determines whether the portion of the assignment message intended for the WT is a low or high power portion of the received assignment message. Next, in step 1826, the WT determines which of a plurality of received target power levels to use for transmitting information to the BS in the assignment segment corresponding to the received assignment message, based on the power level information determined in step 1824. From the determined received target power level, the stored gain factor information corresponding to the determined received target power level, and the power control feedback information, the WT determines a transmit power level required to reach the determined received target power level at the BS in step 1828. Next, in step 1830, the WT transmits a signal to the BS using the determined transmit power level in the assigned uplink channel segment. The transmitted signal will combine in the air with a portion of the signal from another WT to form a portion of a superimposed signal to be received by the BS. The transmitted signal will be the high power signal portion of a superimposed signal received by the BS based on the transmit power level determined if the assignment message intended for the WT is determined to be the low power portion of the assignment message. The transmitted signal will be a low power signal portion of a superimposed signal received by the BS based on the transmit power level determined if the assignment message intended for the WT is determined to be the high power portion of the assignment message. Processing of receiving uplink assignment messages is stopped as transmission of information to the BS in the assigned uplink channel segment is completed, while processing of other assignment messages is started when they are received.

The processing of the downlink channel assignment messages is not described in detail in fig. 18, but such assignment messages may be transmitted using superposition coding in accordance with the present invention.

Although described in the context of an OFDM system, the methods and apparatus of the present invention are applicable to a wide range of communication systems, including many non-OFDM and/or non-cellular systems.

In various embodiments nodes described herein are implemented using one or more modules to perform the steps corresponding to one or more methods of the present invention, such as signal processing, message generation and/or transmission steps. Thus, in some embodiments various features of the present invention are implemented using modules. Such modules may be implemented using software, hardware, or a combination of software and hardware. Many of the above described methods or method steps can be implemented using machine executable instructions, e.g., software, included in a machine readable medium such as a storage device, e.g., RAM, floppy disk, etc. to control a machine, e.g., general purpose computer with or without additional hardware, to implement all or a portion of the above described methods, e.g., in one or more nodes. Accordingly, among other things, the present invention is directed to a machine-readable medium including machine executable instructions for causing a machine, e.g., processor and associated hardware, to perform one or more of the steps of the above-described method(s).

Many additional variations of the methods and apparatus of the present invention described above will be apparent to those skilled in the art in view of the above description of the invention. Such variations are to be considered within the scope of the invention. The methods and apparatus of the present invention may be, and in various embodiments are, used with CDMA, Orthogonal Frequency Division Multiplexing (OFDM), and/or various other types of communications techniques which may be used to provide wireless communications links between access nodes and mobile nodes. In some embodiments the access nodes are implemented as base stations which establish communications links with mobile nodes using OFDM and/or CDMA. In various embodiments the mobile nodes are implemented as notebook computers, Personal Digital Assistants (PDAs), or other portable devices including receiver/transmitter circuits and logic and/or routines, for implementing the methods of the present invention.

Claims (30)

1. A communication method for use in a communication system comprising a base station and a plurality of wireless terminals, a different communication channel existing between each wireless terminal of said plurality of wireless terminals and said base station, said communication channel existing between each particular wireless terminal and said base station having a quality that is the channel quality of said particular wireless terminal, the method comprising:

operating the base station to:

i) storing a set of channel state information indicative of a channel quality of each of said plurality of wireless terminals;

ii) examining said set of channel state information to identify wireless terminals whose channel states differ from each other by at least a preselected minimum value; and

iii) allocating a portion of the communication channel to use to convey superimposed signals corresponding to the identified at least two different wireless terminals having channel conditions differing by at least the preselected minimum.

2. The communication method of claim 1, wherein the communication device is a cellular communication device,

wherein the set of stored channel state information includes signal-to-noise ratio information for the channel;

wherein the at least two different wireless terminals comprise first and second wireless terminals; and

wherein the preselected minimum value by which the channel states of the first and second wireless terminals differ is 3 dB.

3. The method of claim 1, further comprising:

operating the base station to repeat the steps of saving, checking and allocating.

4. The method of claim 1, further comprising:

operating the base station to repeat the steps of saving and checking; and

wherein when the checking step fails to identify at least two wireless terminals having signals to be transmitted in the portion of the communication channel available for allocation and channel conditions differing by a preselected minimum value, the base station is operated to:

assigning the portion of the communication channel available for assignment to a single terminal of the plurality of wireless terminals.

5. The communication method of claim 1, wherein the communication device is a cellular communication device,

wherein the at least two different wireless terminals include a first wireless terminal and a second wireless terminal;

wherein said allocated communication channel portion is a downlink channel portion;

wherein the first wireless terminal has a better channel quality than the second wireless terminal, the method further comprising:

operating said base station to transmit a first superimposed signal to said first and second wireless terminals in said allocated communication channel portion, said first superimposed signal including a low power signal portion intended for said first wireless terminal and a high power signal portion intended for said second wireless terminal, said lower power signal portion being transmitted by said base station at a lower power than said high power signal portion or with less coding protection than said high power signal portion.

6. The communications method of claim 5, wherein said assigned communications channel portion is an assigned channel portion for communicating communications channel portion assignments to wireless terminals.

7. The communication method of claim 6, further comprising:

operating the base station to:

receiving a second superimposed signal from said first and second wireless terminals, said received second superimposed signal comprising first and second signal portions transmitted by said first and second wireless terminals, respectively, said first signal portion being received by said base station at a higher power level than said second signal portion.

8. The communication method of claim 7, further comprising:

operating the base station to:

decoding the first signal portion;

subtracting the first signal component from the second superimposed signal; and

decoding the second signal portion.

9. The communication method of claim 7, further comprising:

operating said first wireless terminal to determine which of a plurality of received target power levels is used to determine a transmit power to use to transmit said first signal portion from said first superimposed signal transmitted to said first and second wireless terminals in said allocated channel portion for communicating communication channel portion assignments to wireless terminals.

10. The communications method of claim 9, wherein operating the first wireless terminal to determine which of a plurality of received target power levels to use comprises:

determining whether a portion of a first superimposed signal used to communicate uplink channel allocation information to the first wireless terminal is transmitted in a low power signal portion or a high power signal portion.

11. A base station for use in a communication system including a plurality of wireless terminals, a different communication channel existing between each wireless terminal of said plurality of wireless terminals and said base station, said communication channel existing between each particular wireless terminal and said base station having a quality of a channel quality of said particular wireless terminal, the base station comprising:

a channel state information group indicating a channel quality of each of the plurality of wireless terminals;

means for examining said set of channel state information to identify wireless terminals whose channel states differ from each other by a preselected minimum value; and

means for assigning a communications channel portion to be used to convey superimposed signals corresponding to at least two different wireless terminals identified as having channel conditions differing by at least said preselected minimum value.

12. A base station according to claim 11, wherein,

wherein the at least two different wireless terminals comprise first and second wireless terminals;

wherein the set of channel state information includes signal-to-noise ratio information for a channel; and

wherein the preselected minimum value by which the channel states of the first and second wireless terminals differ is 3 dB.

13. The base station of claim 11, further comprising:

means for assigning an available communication channel segment to a single one of the plurality of wireless terminals when the means for examining the set of channel state information to identify wireless terminals having channel states that differ from each other by a preselected minimum value fails to identify at least two wireless terminals having signals to be transmitted in the communication channel segment available for assignment and having channel states that differ by the preselected minimum value.

14. The base station of claim 13, wherein said at least two different wireless terminals include first and second wireless terminals, said base station further comprising:

a receiver for receiving a superimposed signal from said first and second wireless terminals, said received superimposed signal including first and second signal portions transmitted by said first and second wireless terminals, respectively, said first signal portion being received by said base station at a higher power level than said second signal portion, said first wireless terminal having a better channel condition than said second wireless terminal.

15. The base station of claim 14, further comprising:

a superposition decoder for decoding said first and second signal portions of said received superposition signal.

16. The base station of claim 15, wherein said superposition decoder comprises:

a decoder device for decoding said first signal portion;

a subtractor for subtracting said first signal portion from said superimposed signal to produce said second signal portion; and

a second decoder device for decoding said second signal portion.

17. A communication method for use in a communication system comprising a base station and a plurality of wireless terminals, a different communication channel existing between each wireless terminal of said plurality of wireless terminals and said base station, said communication channel existing between each particular wireless terminal and said base station having a quality that is the channel quality of said particular wireless terminal, the method comprising:

operating a first wireless terminal having a first channel quality to transmit a first portion of a superimposed communication signal to the base station; and

operating a second wireless terminal having a second channel quality to transmit a second portion of the superimposed communication signal to the base station, the first and second channel qualities differing by at least a first preselected value, the first and second signal portions combining over the air during transmission to the base station to form the superimposed communication signal.

18. The method of communication of claim 17 wherein the first communication channel is a radio channel,

wherein the minimum value of said first pre-selected value by which the channel qualities of the first and second wireless terminals differ is 3 dB.

19. The communications method of claim 17, further comprising:

prior to transmitting said first and second portions of said superimposed communication signal, operating said first and second wireless terminals to receive a superimposed assignment signal including a low power signal portion intended for said first wireless terminal and a high power signal portion intended for said second wireless terminal, said low power signal portion being transmitted by said base station at a lower power than said high power signal portion, said first wireless terminal having a better channel quality than said second wireless terminal, said superimposed assignment signal being used to assign an uplink communication channel portion.

20. The communications method of claim 19, wherein said first and second signal portions transmitted by said first and second wireless terminals, respectively, are transmitted at a power level that causes said first signal portion to be received by said base station at a higher power level than said second signal portion.

21. The communications method of claim 20, further comprising:

operating the first wireless terminal to determine which of a plurality of received target power levels to use to determine a transmit power to use to transmit the first signal portion from the superimposed allocated signal.

22. The communications method of claim 21, wherein operating the first wireless terminal to determine which of a plurality of received target power levels to use comprises:

determining whether a superimposed signal portion used to communicate uplink channel allocation information to the first wireless terminal is transmitted in a low power signal portion or a high power signal portion.

23. A wireless terminal, comprising:

a receiver for receiving a superimposed allocated signal comprising a first signal portion and a second signal portion, one of said signal portions being intended for use by said wireless terminal and another of said signal portions being intended for use by another wireless terminal, said wireless terminal and said another wireless terminal having channel conditions which differ by at least a preselected minimum value, said first signal portion being received at a lower power level than said second signal portion;

a superposition decoder for decoding said first and second signal portions;

means for determining which portion is intended for the wireless terminal based on information contained in one of the first and second signal portions; and

a transmitter for transmitting signals in an uplink communications channel portion corresponding to a received superimposed assignment signal intended for said wireless terminal.

24. The wireless terminal of claim 23, further comprising:

saving receive target level power information for a plurality of different receive power target levels; and

means for determining which of a plurality of receive target power levels to use when transmitting signals in a particular uplink communication channel segment from a received superimposed assignment signal corresponding to the particular uplink communication channel segment.

25. The wireless terminal of claim 23, wherein said means for determining which portion is intended for said wireless terminal based on information contained in one of said first and second signal portions comprises:

determining whether the superimposed signal portion used to convey uplink channel allocation information to the wireless terminal is transmitted in a low power signal portion or a high power signal portion.

26. A communication method for use in a communication system including a base station and a plurality of wireless terminals, a different communication channel existing between each wireless terminal of said plurality of wireless terminals and said base station, said communication channel existing between each particular wireless terminal and said base station having a quality that is the quality of the communication channel quality of said particular wireless terminal, a plurality of signals transmitted from the plurality of wireless terminals to the base station being combined during transmissions between said plurality of wireless terminals and said base station, the method comprising:

operating the base station to:

allocating a portion of an uplink communications channel for simultaneous use by first and second wireless terminals having channel conditions which differ by at least a preselected minimum value;

receiving a composite signal from said uplink communications channel portion, said composite signal comprising a first signal transmitted by said first wireless terminal and a second signal transmitted by said second wireless terminal; and

a superposition decoding operation is performed on the received composite signal to decode the first and second signals included in the composite signal.

27. The communications method of claim 26, wherein operating said base station to allocate an uplink communications channel portion comprises operating the base station to:

selecting a first wireless terminal and a second wireless terminal based on communication channel quality information, said first and second wireless terminals having different wireless terminal communication channel qualities to share an uplink traffic segment; and

wherein the method further comprises operating the base station to:

transmitting information to the selected first and second wireless terminals indicating the assigned traffic channel segment and which of the first and second wireless terminals should transmit signals received by the base station at the higher power level.

28. The method of claim 27, wherein one of the first and second wireless terminals having a better channel condition is to receive at the base station at a higher power level, the method further comprising:

operating said first wireless terminal to transmit a first signal portion in the assigned traffic channel portion to the base station; and

operating said second wireless terminal to transmit a second signal portion in the assigned traffic channel portion to the base station, said first and second signal portions being superimposed during transmission to said base station.

29. The method of claim 28, wherein said first wireless terminal transmits said first signal portion using a lower power than a power used by said second wireless terminal to transmit said second signal portion, but the first signal portion is received by said base station at a higher power level than a power level of the second signal portion received by said base station.

30. The method of claim 29, further comprising

Allocating a communication channel portion, the communication channel portion being part of a downlink channel;

wherein the first wireless terminal has a better channel quality than the second wireless terminal; and

wherein the base station further comprises:

means for transmitting a superimposed signal to the first and second wireless terminals in said allocated communication channel portion, said superimposed signal including a low power signal portion intended for said first wireless terminal and a high power signal portion intended for said second wireless terminal, said low power signal portion being transmitted by said base station at a lower power than said high power signal portion.