HK1149147B - Uplink pilot and signaling transmission in wireless communication systems - Google Patents

Description

Uplink pilot signal and signaling transmission in a wireless communication system

The present application is a divisional application of the chinese patent application entitled "uplink pilot signal and signaling transmission in a wireless communication system" filed as 2003/10/29, application No. 200380102367.4.

RELATED APPLICATIONS

Priority is claimed In this application from U.S. provisional patent application 60/422368 entitled Uplink Pilot and Signaling Transmission In Wireless Communication Systems, filed on 29.10.2002 and U.S. provisional patent application 60/422362 entitled channel estimation for OFDM Communication Systems, filed on 29.10.2002, both of which are incorporated herein by reference.

Technical Field

The present invention relates generally to data communication, and more specifically to techniques for transmitting pilot signals and signaling (e.g., rate control) information via an uplink in a wireless communication system.

Technical Field

Wireless communication systems are widely deployed to provide various types of communication such as voice, packet data, and so on. These systems may be multiple-access systems capable of supporting sequential or simultaneous communication with multiple users by sharing the available system resources. Examples of such systems include: code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, and Orthogonal Frequency Division Multiple Access (OFDMA) systems.

An OFDM system employs Orthogonal Frequency Division Multiplexing (OFDM), effectively dividing the overall system bandwidth into a number (N) of orthogonal subbands. These subbands are also called tones (tones), frequency bins (frequency bins), and frequency subchannels. Each sub-band may be considered an independent transmission channel that may be used to transmit data.

In a wireless communication system, an RF modulated signal from a transmitter reaches a receiver via multiple propagation paths. The characteristics of the propagation path typically change over time due to a number of factors. For an OFDM system, the N subbands may experience different channel conditions and may achieve different signal-to-noise ratios (SNRs).

In order to efficiently transmit data on the available subbands, it is often necessary to accurately estimate the wireless channel response between the transmitter and the receiver. Typically, channel estimation is performed by transmitting a pilot signal from a transmitter and measuring the pilot signal at a receiver. Since the pilot signal is made up of symbols known a priori by the receiver, the channel response can be estimated as the ratio of the received pilot symbols to the transmitted pilot symbols.

Pilot signal transmission represents overhead (overhead) in a wireless communication system. Therefore, it is desirable to reduce pilot signal transmission to as small an extent as possible. However, due to the presence of noise and other interference (artifacts) in the wireless channel, a sufficient amount of pilot signal needs to be transmitted in order for the receiver to obtain a reasonably accurate estimate of the channel response. Furthermore, since the effect of the propagation path on the channel response and the propagation path itself typically vary over time, repeated pilot signal transmissions are required. The duration of time during which a wireless channel is assumed to be relatively stable is often referred to as the channel coherence time (channel coherence time). To maintain high system performance, the interval between repeated transmissions of the pilot signal should be significantly less than the channel correlation time.

In the downlink of a wireless communication system, multiple terminals use a single pilot signal transmitted from an access point (or a base station) to estimate the response of different channels from the access point to the terminals. In the uplink, it is often necessary to estimate the channel from each terminal to the access point through a separate pilot signal transmitted from each terminal.

Therefore, for a wireless communication system, multiple terminals each need to transmit a pilot signal over the uplink to the access point. In addition, signaling information, such as rate control information and acknowledgements for downlink transmissions, also need to be sent over the uplink. If uplink transmission is performed in a Time Division Multiplexing (TDM) manner, each terminal may be assigned a different time slot and then transmit its pilot signal and signaling information in the assigned time slot. Depending on the number of active terminals and the duration of the time slot, a significant portion of the uplink transmission time may be occupied by pilot signals and signaling transmissions. This inefficiency in the uplink transmission of pilot signals and signaling information is further exacerbated in OFDM systems, where the data carrying capacity of the smallest transmission unit (typically one OFDM symbol) may be large.

Accordingly, there is a need in the art for techniques to more efficiently transmit pilot signals and signaling information in a wireless communication system, such as an OFDM system.

Disclosure of Invention

Techniques are provided herein for more efficient transmission of pilot signals and signaling over an uplink in a wireless communication system. Through subband multiplexing, the M usable subbands in the system may be divided into Q disjoint groups of subbands, where if any subband is included in a group, it is only included in one and only one group. Each subband group may then be assigned to a different terminal. Multiple terminals may transmit signals simultaneously on their assigned channels.

With subband multiplexing, each terminal may obtain accurate channel estimates for all available subbands based on only the uplink pilot signals transmitted in a small subset of the available subbands. If the total energy used to transmit the pilot signal on the S subbands is maintained equal to the total energy used to transmit the pilot signal on all M usable subbands, then the channel responses of the other M-S subbands may be accurately interpolated using only the pilot signals transmitted on the S subbands.

One embodiment provides a method of transmitting pilot signals over an uplink in a wireless communication system, such as an OFDM system, having a plurality of subbands. According to the method, M usable subbands suitable for data transmission in the system are initially divided into Q disjoint groups of subbands. The Q groups may include the same or different number of subbands, and the subbands in each group may be uniformly or non-uniformly distributed among the M usable subbands. Each of the one or more terminals is assigned a different subband group for uplink pilot signal transmission. Pilot signals transmitted from the one or more terminals are then received on the assigned subband group. The pilot signal transmit power in each subband may be adjusted higher (e.g., by a factor of Q) for each terminal so that the same total pilot signal energy is achieved even when the pilot signal is transmitted on S, rather than M, subbands. Power adjustments are performed such that the total available transmit power is observed at each terminal, transmit power constraints (e.g., adjustment constraints) are satisfied, and the amount of cost increase of the hardware portion is minimized (if the cost increases). Each terminal then obtains a channel estimate based on the pilot signals received on the subbands assigned to that terminal. The channel estimate for each terminal may cover one or more other subbands not included in the group assigned to that terminal. For example, the channel estimate may include responses to all M usable subbands.

Subband multiplexing may also be used to transmit signaling information on the uplink. The signaling information may include: rate control information for downlink data transmission, acknowledgements for receiving data on the downlink, and so on.

Various aspects and embodiments of the invention are described in further detail below.

Brief Description of Drawings

The features, nature, and advantages of the present invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings in which like reference characters designate like or corresponding functions and features, and in which:

FIG. 1 illustrates an OFDM system supporting multiple users;

FIGS. 2, 3 and 4 show a frame structure, an OFDM subband structure, and an OFDM subband structure supporting subband multiplexing, respectively;

FIG. 5 illustrates a process for transmitting uplink pilot signals using subband multiplexing;

FIG. 6 shows a frame structure for subband multiplexing supporting uplink pilot and signaling transmission;

FIG. 7 is a block diagram of an access point and a terminal in an OFDM system; and

figures 8A to 8C show diagrams of potential savings achieved by subband multiplexing for uplink pilot signal and signaling transmission.

Detailed Description

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Embodiments or designs described herein as "exemplary" are not intended to be preferred or advantageous over other embodiments or designs.

The techniques described herein for transmitting pilot signals and signaling information may be used in various types of wireless communication systems. For example, these techniques may be used for CDMA, TDMA, FDMA and OFDM systems. These techniques may also be used in hybrid systems, such as OFDM TDM systems, which transmit pilot signals/signaling and traffic data using time division multiplexing, where OFDM is used to transmit pilot signals/signaling and another transmission mechanism is used to transmit traffic data. For clarity, these techniques are described in detail below for an OFDM system.

Fig. 1 shows an OFDM system 100 supporting multiple users. OFDM system 100 includes a plurality of Access Points (APs) 110 that support communication with a plurality of terminals (T) 120. For simplicity, only one access point is shown in fig. 1. An access point is also referred to as a base station or other terminology.

Terminals 120 may be distributed throughout the system. A terminal is also called a mobile station, a remote station, an access terminal, a User Equipment (UE), a wireless device, or other terminology. Each terminal is a fixed or mobile terminal that may communicate with one or possibly multiple access points via the downlink and/or uplink at any given time. The downlink (or forward link) refers to transmission from the access point to the terminal, and the uplink (or reverse link) refers to transmission from the terminal to the access point.

In fig. 1, the access point 110 communicates with the user terminals 120a to 120f via uplink and downlink. Depending on the particular design of an OFDM system, an access point may communicate with multiple terminals simultaneously (e.g., via multiple subbands) or sequentially (e.g., via multiple slots).

Fig. 2 shows a frame structure 200 that an OFDM system may use when both uplink and downlink use a single frequency band. In this case, the downlink and uplink may share the same frequency band using Time Division Duplexing (TDD).

As shown in fig. 2, uplink and downlink transmission is performed in units of "MAC frames". Each MAC frame may be defined to cover a particular duration. Each MAC frame is divided into a downlink phase 210 and an uplink phase 220. Downlink transmissions to multiple terminals may be multiplexed using Time Division Multiplexing (TDM) in the downlink phase. Also, uplink transmissions from multiple terminals may be multiplexed using TDM in the uplink phase. For the particular TDM implementation shown in fig. 2, the stages are further divided into a plurality of time slots (or simply slots) 230. The duration of these time slots may be fixed or variable, and the duration of the time slots of the uplink and downlink phases may be the same or different. For this particular TDM implementation, each time slot 230 in the uplink phase includes a pilot signal segment 232, a signaling segment 234, and a data segment 236. Segment 232 is used to transmit uplink pilot signals from the terminals to the access point, segment 234 is used to transmit signaling (e.g., rate control, acknowledgement, etc.), and segment 236 is used to transmit data.

The time slots in the uplink phase of each MAC frame may be allocated to one or more terminals for uplink transmission. Each terminal then transmits a signal through the time slot assigned to it.

The frame structure 200 represents one specific implementation used by an OFDM system when only one frequency band is available. If two frequency bands are available, frequency division multiplexing (FDD) may be used, with uplink and downlink transmissions over different frequency bands. In this case, the downlink phase may be implemented on one frequency band and the uplink phase on another frequency band.

Both TDD-based and FDD-based frame structures may use the pilot signal and signaling transmission techniques described herein. For simplicity, the techniques are described with particular reference to TDD-based frame structures.

Fig. 3 shows an OFDM subband structure 300 used by an OFDM system. The overall system bandwidth of the OFDM system is W MHz, which is divided into N orthogonal subbands by using OFDM. The bandwidth of each sub-band is W/N MHz. Of the N total subbands, only M subbands are used for data transmission, where M < N. The remaining N-M subbands are unused and serve as guard bands (guard bands) to allow the OFDM system to meet its spectral mask requirements. The M "available" subbands include subbands F through M + F-1.

For OFDM, the data to be transmitted on each subband is first modulated (i.e., symbol mapped) using a particular modulation scheme selected for each subband. For the N-M unused subbands, the signal value is set to 0. For each symbol period, the M modulation symbols and N-M zeros of all N subbands are transformed to the time domain using an Inverse Fast Fourier Transform (IFFT), thereby obtaining a transformed symbol that includes N time-domain samples. The duration of each symbol after the transform is inversely proportional to the bandwidth of each subband. For example, if the system bandwidth is W-20 MHz and N-256, the bandwidth of each sub-band is 78.125KHz, and the duration of each symbol after conversion is 12.8 μ s.

OFDM may provide certain advantages, such as the ability to suppress frequency selective fading, which is characterized by different channel gains at different frequencies across the system bandwidth. It is well known that frequency selective fading produces inter-symbol interference (ISI), a phenomenon in which each symbol in a received signal distorts subsequent symbols in the received signal. ISI distortion affects the ability to correctly detect the received symbols and therefore results in reduced performance. Frequency selective fading can be conveniently suppressed with OFDM by repeating (or appending a cyclic prefix to) a portion of each symbol after transformation to form a corresponding OFDM symbol and then transmitting it.

The length (i.e., the amount of repetition) of the cyclic prefix per OFDM symbol depends on the delay spread (delayspread) of the wireless channel. For a given transmitter, the delay spread is the difference of the earliest and latest arriving signal instances at the receiver for the signal transmitted by that transmitter. The delay spread of the system is the worst case delay spread expected for all terminals in the system. In order to effectively suppress ISI, the cyclic prefix should be longer than the delay spread.

Each transformed symbol is N sample periods in duration, where each sample period is (1/W) μ s in duration. A cyclic prefix may be defined to include Cp samples, where Cp is an integer selected according to the expected delay spread of the system. Specifically, Cp is selected to be greater than or equal to the number of taps (L) of the impulse response of the wireless channel (i.e., Cp ≧ L). In this case, each OFDM symbol will include N + Cp samples, and each symbol period is N + Cp sample periods.

Uplink pilot signal transmission

In some OFDM systems, terminals transmit pilot signals over the uplink for the access point to estimate the uplink channel. If the TDD-TDM frame structure shown in fig. 2 is used, each terminal may transmit its uplink pilot signal in the pilot signal segment of its assigned time slot. Typically, each terminal transmits an uplink pilot signal at full power (fullpower) in all M available subbands. In this way, the access point can estimate the uplink channel response for the entire available frequency band. Although this uplink pilot transmission mechanism is effective, its efficiency is low because all active terminals may use a significant portion of the uplink phase for pilot transmission. The pilot signal segments for all active terminals may include a significant portion of the uplink phase.

Techniques are provided herein to more efficiently transmit pilot signals over the uplink in an OFDM system. To be more efficient, the pilot signal transmission scheme needs to be designed as: each active terminal may achieve accurate channel estimation based on the uplink pilot signals transmitted from the terminals. However, it has been found that the quality of the channel estimate is typically dependent on the total energy of the pilot signal, rather than the specific details of the pilot signal transmission scheme. The total pilot signal energy is equal to the transmit power used for the pilot signal multiplied by the duration of pilot signal transmission.

Accurate channel estimation for all available bands can be achieved from pilot signals transmitted on only S subbands, where S is chosen such that Cp ≦ S < M, and S is typically much less than M. One such channel estimation technique is described in the above-mentioned U.S. provisional patent application serial No. 60/422368, U.S. patent application serial No. 60/422362, and U.S. patent application docket No. 020718. In practice, it can be seen that if the total energy used to transmit the pilot signal on the S subbands is equal to the total energy used to transmit the pilot signal on all M subbands, then the channel responses of the other M-S subbands can be accurately interpolated from the pilot signal transmitted on the S subbands using the channel estimation technique described above. In other words, if the total energy of the pilot signal is the same, then the channel responses of the inserted M-S subbands are typically of the same quality (e.g., the same average variance) as the channel estimates obtained from the pilot signals transmitted on all M subbands.

Multiple terminals may transmit pilot signals simultaneously on the uplink via subband multiplexing. To implement subband multiplexing, the M usable subbands may be divided into Q disjoint groups of subbands such that if any usable subband occurs in a group, it only occurs in one group. The Q groups may include the same or different number of subbands, and the subbands in each group may be uniformly or non-uniformly distributed among the M usable subbands. It is also not necessary to use all M subbands in the Q group (i.e., some of the available subbands may not be used for pilot transmission).

In one embodiment, each group includes S subbands, where,and S is not less than Cp, wherein,representing the floor operator. The number of subbands in each group should be equal to or greater than the delay spread Cp so that the influence of ISI can be reduced and more accurate channel estimation can be achieved.

Fig. 4 illustrates one embodiment of an OFDM pilot signal structure 400 that may be used for an OFDM system and supports subband multiplexing. In this embodiment, the M usable subbands are initially divided into S disjoint sets, each set including Q consecutive subbands. The Q subbands in each set are assigned to Q groups such that the ith subband in each set is assigned to the ith group. Thus, the S subbands in each group are uniformly distributed across the M usable subbands, such that consecutive subbands in the group are separated by Q subbands. The M subbands may be assigned to the Q groups in other manners, which also falls within the scope of the present invention.

The Q subband groups may be assigned to up to Q terminals for uplink pilot signal transmission. Each terminal then transmits a pilot signal on the subbands assigned to it. With subband multiplexing, up to Q terminals may transmit pilot signals simultaneously on the uplink on up to M usable subbands. This may greatly reduce the amount of time required to transmit the uplink pilot signal.

In order for the access point to obtain a high quality channel estimate, each terminal may increase the transmit power per subband by a factor of Q. This allows the pilot signal total energy of the pilot signal transmitted on these S subbands to be allocated the same as in the case where all M subbands are used for pilot signal transmission. Since the total energy of the pilot signal is the same, the access point can estimate the channel response for all of the available frequency bands based on a subset of the M available subbands with little or no loss in quality, as will be described below.

An OFDM system can operate in a band with a power constraint of P dBm/MHz per MHz and a total power constraint of P · W dBm. For example, the 5GHz UNII band includes three 20MHz bands, denoted UNII-1, UNII-2, and UNII-3, respectively. The total transmit power limits for these three bands are 17, 24 and 30dBm, respectively, and the power constraints per MHz are 4, 11 and 17dBm/MHz, respectively. From the lowest power constraints of the three bands, the power constraint per terminal can be chosen such that the power constraint per MHz is 4dBm/MHz and the total power constraint is 17 dBm.

These subband groups are formed such that uplink pilot signal transmission can be performed using full transmit power, even if a power constraint per MHz and a total power constraint are imposed on each terminal. In particular, if the spacing between subbands in each group is about 1MHz, each terminal may transmit uplink pilot signals in all S subbands assigned to it with a power per subband of P dBm and still follow the power per MHz constraint. The total transmitted power of these S subbands will then be equal to P · S dBm, which is approximately equal to P · W dBm due to the 1MHz spacing, S ≈ W. In general, as long as S > W, where W is given in MHz, the power constraint per MHz and the total power constraint can be met with appropriate adjustments.

In an exemplary OFDM system, the system bandwidth is W-20 MHz, N-256, and M-224. The OFDM pilot signal structure includes Q-12 groups, each group including S-18 subbands. For this pilot signal structure, 216 subbands out of 224 usable subbands may be used simultaneously for uplink pilot signal transmission, with the remaining 8 subbands not being used.

In general, the amount of transmit power used by each subband in each group depends on various factors, such as: (1) a power constraint and a total power constraint per MHz, and (2) a subband distribution in each group. The terminal may transmit the uplink pilot signal at full power even if the spacing between subbands is not uniform and/or less than 1 MHz. Then, from the subband distributions in the Q groups, the specific amount of power for the subbands can be determined. For simplicity, it is assumed that the S subbands in each group are uniformly spaced and separated by a desired minimum spacing (e.g., at least 1 MHz).

Figure 5 is a flow diagram of one embodiment of a process 500 for transmitting uplink pilot signals using subband multiplexing. Initially, the M usable subbands are divided into Q disjoint groups of subbands (step 512). This division may be performed once according to the expected load in the OFDM system. Alternatively, the M usable subbands may be dynamically divided as system load changes. For example, when the system load is light, fewer groups are formed, and when the system load is peak, more groups are formed. In each case, the partitions are such that each group satisfies the condition S ≧ Cp.

One subband group is assigned to each active terminal for uplink pilot signal transmission (step 514). The subband assignment may be determined at call setup or later and communicated to the terminal. Each terminal then transmits signals on the uplink in the sub-bands assigned to it (step 522). Each terminal may increase the transmit power used for uplink pilot signal transmission by an amount of transmit power for each subband determined based on the various factors described above. The access point may also specify an amount of transmit power to use for each subband (or group of subbands) and transmit it to the terminals along with the subband assignments.

The access point receives the uplink pilot signals transmitted from all active terminals on all M available subbands, or a subset thereof (step 532). The access point then processes the received signals to obtain per-subband channel estimates for the subbands assigned to each active terminal (step 534). For each active terminal, channel estimates for all available frequency bands may be obtained based on the per-subband channel estimates obtained for each assigned subband (step 536). Channel estimates for the entire available frequency band may be obtained from channel estimates for a portion of the available subbands using various techniques. One such channel estimation technique is described in the above-mentioned U.S. provisional patent application serial No. 60/422368, U.S. provisional patent application serial No. 60/422362, and U.S. patent application docket No. 020718. Channel estimates for the entire available frequency band may also be obtained by interpolating channel estimates for each subband of a subset of the available subbands.

For each active terminal, the channel estimates for all available frequency bands are then available for downlink and/or uplink data transmission to/from that terminal (step 538). Uplink pilot signal transmission and channel estimation are typically performed continuously during a communication session to obtain the most up-to-date channel estimate.

The OFDM system model can be expressed as:

r＝Hox+nequation (1)

Wherein the content of the first and second substances,ris a vector having N terms representing symbols received on the N subbands;

xis a vector having N entries representing symbols transmitted on the N subbands (some entries may include zeros);

His a (N × 1) vector representing the channel frequency response between the access point and the terminal;

nis an Additive White Gaussian Noise (AWGN) vector for the N subbands; and is

"o" represents the Hadmard product (i.e., a dot product, where,rthe ith element of (a) isxAndHthe product of the ith element of).

Hypothesis noisenHas a mean value of 0 and a variance of σ²。

Each active terminal transmits pilot signals on its assigned S subbands in a pilot signal transmission interval through subband multiplexing, the pilot signal transmitted by each terminal may be represented as a (N × 1) vectorx _iWhich includes the pilot symbol for each of the assigned S subbands and 0 for all other subbands. The transmit power of the pilot symbols on each assigned subband may be expressed asWherein x is_i，jIs the pilot symbol transmitted by terminal i on the jth subband.

Per-subband channel estimation for terminal iCan be expressed as:

formula (2)

Wherein the content of the first and second substances,is a (S × 1) vector,a _i/b _i＝[a₁/b₁……a_s/b_s]^Twhich includes the ratio of S subbands assigned to terminal i. Per-subband channel estimation for terminal iDetermined by the access point based on the pilot symbols received and transmitted by each of the S subbands assigned to the terminal. Therefore, per-subband channel estimationRepresenting the channel frequency response of the assigned S subbands for terminal i.

Channel estimation from each subband may be performed using a number of techniquesGet the pair in formula (1)HIs estimated. As noted above, one such technique is described in U.S. provisional patent application serial No. 60/422368, U.S. provisional patent application serial No. 60/422362, and U.S. patent application docket No. 020718.

If N subbands are all used for data transmission (i.e., M ═ N), then it can be seen that the Mean Square Error (MSE) of the channel estimates obtained from pilot signal transmission on only S subbands is the same as the MSE of the channel estimates obtained from pilot signals transmitted on all N subbands, using the techniques described in the above-mentioned U.S. provisional patent application serial No. 60/422368, U.S. provisional patent application serial No. 60/422362, and U.S. patent application docket No. 020718, if the following conditions are met:

1. selecting S to be not less than Cp and S to be not less than W;

2. the S subbands are uniformly distributed in each group of all N subbands;

3. setting the transmission power of each of the S allocated subbands to be higher than an average transmission power P defined as follows_avgN/S times of.

The total transmit power used by a terminal to transmit is typically constrained by the lesser of: (1) total transmission power P of terminal_total(limited by the power amplifier of the terminal) and (2) a total power constraint P · W of the operating band. Thus, the average transmission power P_avgIs equal to P_tota1The smaller of/N and P.W/N. For example, if the total transmit power used by the terminal is limited by the regulatory constraint, then P_avg＝P·W/N。

If only a subset of the N total subbands are used for data transmission (i.e., M < N), in which case some subbands are used as guard bands, then Minimum Mean Square Error (MMSE) can only be achieved if S ═ M. However, it has been found in the above U.S. provisional patent application No. 60/422368, U.S. provisional patent application No. 60/422362, and U.S. patent application No. 020718: if S ≈ 1.1Cp, the MSE approaches the MMSE. Thus, in the case of S ≦ M < N, the MSE of the channel estimate obtained from pilot signal transmission on only S subbands is minimal if the following conditions are met:

1. selecting S to be approximately equal to 1.1Cp, wherein S is more than W;

2. the S subbands are uniformly distributed in each group of N total subbands;

3. setting the transmission power of each of the allocated S sub-bands to be higher than the average transmission power P_avgN/S times of.

Uplink signaling transmission

In many wireless systems, a terminal needs to send signaling information to an access point over an uplink. For example, the terminal may need to inform the access point of the rate for downlink data transmission, send an acknowledgement of received data packets, and so on. The signaling information typically includes a very small amount of data, but needs to be sent timely and possibly periodically.

In some systems, it may be desirable to send rate control information over the uplink to indicate the rate used on the downlink for each of one or more transport channels. Each transmission channel may correspond to a spatial subchannel (i.e., a eigenmode) in a multiple-input multiple-output (MIMO) system, a subband or frequency subchannel in an OFDM system, a time slot in a TDD system, etc. Each terminal may estimate the downlink channel and determine the highest rate that each transport channel can support. Rate control information for the transport channel may then be sent back to the access point and used to determine the transmission rate of the downlink data for transmission to the terminal. The rate control information may be in the form of one or more rate codes, each of which may be mapped to a specific combination of code rate, modulation scheme, etc. Alternatively, the rate control information may be provided in other forms (e.g., received SNRs for the respective transmission channels). In any case, the rate control information for each transport channel includes 3 to 4 bits, and the rate control information for all transport channels may include 15 bits in total.

As another example, channel response or frequency selectivity information needs to be reported back to the access point. The number of bits required for the channel response or frequency selectivity information depends on the granularity of the information being transmitted (e.g., per subband or per nth subband).

Techniques for more efficiently transmitting signaling information over an uplink in an OFDM system are also provided herein. The M usable subbands may be divided into Q_RDisjoint groups, each usable subband if present in a groupIt is only present in one group. This Q_RThe number of subbands included in a group may be the same or different. The grouping of the available subbands for uplink signaling information and the grouping of the available subbands for uplink pilot signal transmission may be the same or different. Each subband group may be assigned to a terminal for uplink signaling transmission. Multiple terminals may transmit signaling information simultaneously on the subbands assigned to them.

The transmission of uplink signaling information by subband multiplexing has various advantages. Since the data carrying capacity of an OFDM symbol is relatively large, allocating the entire OFDM symbol to an active terminal may result in inefficiencies when only a small amount of data needs to be transmitted. By subband multiplexing, the number of subbands assigned to each active terminal is proportional to the amount of data to be transmitted.

The savings from subband multiplexing are even greater if the transmit power per subband is increased by the number of terminals multiplexed in the same time interval. The higher the transmit power per subband, the higher the received SNR of the access point, which can support higher order modulation schemes. In this way, more data or information bits can be transmitted on each subband. Alternatively, fewer subbands may be assigned to each terminal, so that more terminals may be multiplexed in the same time interval. If a higher order modulation scheme is used, then fewer subbands can provide the required data carrying capability.

Subband multiplexing may also be used to transmit acknowledgement information over the uplink. For some systems, the receiver needs to send an acknowledgement to confirm that the detection of the groups received by the receiver is correct or incorrect. System efficiency may be improved by reducing the granularity of allocation of resources for transmitting acknowledgement information (i.e., allocating one subband group to each terminal instead of an entire OFDM symbol).

The amount of data sent to acknowledge varies from terminal to terminal and from frame to frame. The reason is that: each terminal typically transmits only acknowledgement information for packets received within the current/previous MAC frame, and the number of packets transmitted to each terminal varies with terminal and time. In contrast, the amount of data sent for rate control is generally more constant.

A variety of subband allocation schemes may be used to transmit a variable amount of signaling (e.g., acknowledgment information) on the uplink between active terminals. In one scheme, the M usable subbands are divided into Q_AA disjoint group. This Q_AThe number of subbands included in a group may be the same or different. Each active terminal may be assigned a variable number of subbands for acknowledgement information transmission. For such a scheme, the number of subbands assigned to a particular terminal may be proportional to the number of groups transmitted to that terminal.

In another scheme, the number of subbands assigned to each active terminal for transmitting acknowledgment information is fixed. However, the modulation scheme used by each terminal is not fixed, but may be selected according to channel conditions. For a complementary channel (reciprocal channel), its uplink and downlink are highly correlated, as are downlink and uplink transmission capacities. Thus, if more data packets can be sent on the downlink within a certain time period due to increased channel conditions, the same channel conditions can support more information bits being transmitted on the uplink within a certain time interval. In this way, by allocating a fixed number of subbands to each active terminal, but allowing modulation to adapt according to channel conditions, more acknowledgment bits can be transmitted when needed.

To simplify the allocation of subbands to active terminals, subbands may be divided into groups and then groups of subbands, rather than individual subbands, may be allocated to the terminals. In general, each group may include any number of subbands, depending on the desired granularity of subband allocation. As an example, 37 subband groups may be formed, each group comprising 6 subbands. Any number of subband groups may then be assigned to a given terminal based on data requirements.

For a particular OFDM system design, 150 to 2000 bits may be transmitted in two OFDM symbols, within the range of rates supported by the system. The bit rate range is obtained on the assumption that: with subband multiplexing, higher transmit power is used for each subband. Then, each of the 37 subband groups described in the above example may be used to transmit 150/37 to 2000/37 acknowledgment bits depending on channel conditions. Thus, a fixed number of subbands in each group may transmit a variable number of acknowledgement bits, depending on the rate selected for use, which may depend on channel conditions.

In some cases, the transmit power per subband needs to be maintained at the same level as the data transmission. This may occur, for example, if all available subbands are allocated to a single terminal. However, when the data carrying capacity of a sub-band is low, the requirements on it are correspondingly reduced. For all channel configurations desired, two OFDM symbols are sufficient for acknowledgement data.

In another scheme, acknowledgement data is sent with uplink packet data. Additional delay may occur if the acknowledgment data needs to wait for packet data to be sent on the uplink. If the additional delay is tolerable, there is little overhead in sending the acknowledgement data, since the amount of acknowledgement data is typically small and likely fits into the padding portion of the uplink data packet.

In another arrangement, the acknowledgment data is sent with the rate control information. The subband groups assigned to each active terminal for rate control transmission may have a data-carrying capacity that is higher than the data-carrying capacity required to transmit the rate control information. In this case, the acknowledgment data may be sent in excess data carrying capacity of the sub-band allocated for rate control.

When transmitting signaling information over the uplink using subband multiplexing, the access point may process the received signals to recover the signaling (e.g., rate control and acknowledgement) sent by each terminal on a per-terminal basis.

Example frame Structure for subband multiplexing

Fig. 6 illustrates one embodiment of a frame structure 600 that supports subband multiplexing for uplink pilot and signaling transmission. The MAC frame is divided into a downlink phase 610 and an uplink phase 620. The uplink phase is further divided into a pilot signal segment 622, a signaling segment 624, and a plurality of time slots 630. Segment 622 may use subband multiplexing so that multiple terminals may transmit pilot signals simultaneously on the uplink in the segment. Similarly, segment 624 may use subband multiplexing so that multiple terminals may transmit signaling (e.g., rate control information, acknowledgements, etc.) simultaneously on the uplink in the segment. Time slots 630 may be used to transmit packet data, messages, and other information. Each time slot 630 may be allocated to one or more active terminals with or without subband multiplexing. Each slot 630 may also be used to send overhead messages to multiple terminals.

Various other frame structures may be devised and are within the scope of the present invention. For example, the uplink phase includes a rate control segment for transmitting rate control information and an acknowledgement segment for transmitting acknowledgement data. As another example, the frame may be divided into multiple uplink and downlink phases, and different phases may be used for different types of transmissions, such as traffic data, pilot signals, rate signaling, and acknowledgements.

Implementation considerations

Subband multiplexing may greatly reduce the amount of resources required to support the transmission of pilot signals and signaling on the uplink, which may be quantified below. However, various factors need to be considered when implementing subband multiplexing, such as: (1) overhead signaling for allocating subbands to terminals; (2) a time offset between uplink transmissions received from the terminals; (3) frequency offset between uplink transmissions from the terminal. Each of these factors will be described in detail below.

Overhead signaling

Communicating the subband assignments for each terminal requires overhead signaling. For both pilot signals and rate control information, each active terminal may be assigned a particular subband group for each or both of the two types of uplink transmissions. Such assignments may be made during call setup, and the assigned subbands typically do not have to be repeated or changed for each MAC frame.

If there are 24 subband groups for a maximum of 24 terminals, then 5 bits are sufficient to identify the particular subband group assigned to a terminal. These 5 bits may be included in a control message sent to the terminal to bring it into an active state. If the control message is 80 bits in length, then 5 bits used to represent the sub-band allocation would increase the message length by approximately 6%.

The amount of overhead signaling may be greater if the subband groups may be flexibly formed and/or if the groups may be dynamically allocated to terminals. For example, if the number of subbands allocated for acknowledgment transmission may vary from frame to frame, the amount of overhead signaling required to convey the subband allocation may be greater.

Uplink timing

Multiple terminals transmitting signals simultaneously via subband multiplexing may be dispersed throughout the system. If the terminals are at different distances from the access point, the propagation times of the signals transmitted from the terminals will be different. In this case, if the terminals transmit signals simultaneously, the access point will receive signals from these terminals at different times. The difference between the earliest and latest arriving signals at the access point depends on the difference in round trip (round trip) delay of the terminal relative to the access point.

The difference in arrival times of signals from different terminals violates the delay spread tolerance of the terminals that are farther away (cut into). For example, for an access point having a coverage area with a radius of 50 meters, the maximum difference in arrival time between the earliest and latest arriving signals is about 330ns, which would occupy a significant portion of the 800ns cyclic prefix. Furthermore, the effect of reduced delay spread tolerance is worst for terminals at the edge of the coverage area, which are highly required to accommodate multipath delay spread.

In one embodiment, to account for the difference in round-trip delay between active terminals, the uplink timing of each active terminal is adjusted so that its signal arrives at the access point within a particular time window (timewindow). A timing adjustment loop is maintained for each active terminal and the round trip delay for that terminal is estimated. The uplink transmissions of the terminals are then advanced or delayed by an amount determined based on the estimated round trip delay so that the uplink transmissions of all active terminals can reach the access point within a particular time window.

The timing adjustment for each active terminal may be obtained based on a pilot signal from the terminal or some other uplink transmission. For example, the uplink pilot signal can be associated with a copy of the pilot signal of the access point. The correlation result indicates that the received pilot signal is earlier or later than the pilot signals from other terminals. A 1-bit timing adjustment value may then be sent to the terminal to indicate that it will advance or delay the time by a particular amount (e.g., ± one sample period).

Frequency offset

If subband multiplexing is used to allow multiple terminals to transmit signals simultaneously on their assigned subbands, signals from nearby terminals may cause significant interference to signals from distant terminals if all terminals transmit at full power. In particular, it can be seen that frequency offsets between terminals can produce inter-subband interference. Such interference may cause channel estimates obtained from the uplink pilot signal to degrade and/or may increase the Bit Error Rate (BER) of the uplink data transmission. In order to reduce the influence of inter-subband interference, power control is performed on a terminal so that a nearby terminal does not generate excessive interference to a distant terminal.

The impact of interference from nearby terminals is studied and it is found that power control can be used roughly to reduce the inter-subband interference impact. In particular, it was found that if the maximum frequency offset between terminals is 300Hz or less, the loss of SNR of other terminals is 1dB or less by limiting the SNR of nearby terminals to 40dB or less. If the frequency offset between terminals is 1000Hz or less, then to ensure that the SNR loss of other terminals is 1dB or less, the SNR of nearby terminals needs to be limited to 27 dB. If the SNR required to achieve the highest rate supported by the OFDM system is less than 27dB, then the SNR for nearby terminals is limited to 27dB (or 40dB) without any impact on the highest data rate supported by nearby terminals.

The coarse power control requirement may be implemented with a slow power control loop. For example, control messages may be sent when there is a need to adjust the uplink power of nearby terminals (e.g., when the power levels of these terminals change due to movement). When accessing the system (as part of call setup), each terminal may know the initial transmit power level for the uplink.

Groups of subbands may be assigned to active terminals in a manner that reduces the impact of inter-subband interference. Specifically, a terminal having a high received SNR is allocated adjacent subbands. Terminals with low SNR are assigned adjacent subbands but far away from those assigned to terminals with high received SNR.

Overhead savings for subband multiplexing

The ability to transmit up to Q uplink pilot signals simultaneously reduces the pilot signal overhead by up to Q times. Since the uplink pilot signal transmission will occupy a significant portion of the uplink phase, the improvement is considerable. The amount of improvement can be quantified by an exemplary OFDM system.

In this exemplary OFDM system, the system bandwidth is W-20 MHz and N-256. Each sampling period has a duration of 50 ns. The cyclic prefix used is 800ns (or Cp-16 samples) and the duration of each OFDM symbol is 13.6 μ s (or N + Cp-272 samples). The uplink pilot signal is transmitted within each MAC frame, each MAC frame being 5ms or 367 OFDM symbols in duration. The pilot signal transmitted from each terminal needs to have a total energy of 4 symbol periods x full transmit power. If there are K active terminals, then the total number of symbol periods required to transmit the pilot signal without subband multiplexing is 4 · K. For the case of K-12, transmitting the uplink pilot signal would use 48 symbol periods, which would occupy about 13.1% of the 367 symbols in the MAC frame. If there are 24 active terminals, the pilot signal overhead would increase to 26.2% of the MAC frame.

If K active terminals are assigned to K subband groups and allowed to transmit uplink pilot signals simultaneously, only 4 symbol periods are required for uplink pilot signals within each MAC frame. When subband multiplexing is used for the uplink pilot signal, the overhead can be reduced to 1.1% of the MAC frame for the case of K12, and 2.2% for K24. This represents a significant savings of 12% and 24% in the amount of overhead required for uplink pilot signal transmission for the cases of K12 and K24, respectively.

Fig. 8A is a diagram of the amount of savings in uplink pilot signal transmission for different numbers of active terminals in the exemplary OFDM system described above. As shown in fig. 8A, the amount of saving increases approximately linearly with the number of terminals.

Supporting Q_RThe savings of an exemplary OFDM system with simultaneous uplink rate control transmissions may also be quantified. The exemplary OFDM system has M-224 usable subbands and is modulated using BPSK encoded at rate 1/3. Each modulation symbol has 1/3 information bits, and approximately 75 information bits may be transmitted on the 224 usable subbands in each symbol period. If each terminal transmits 15 bits or less of rate control information within each MAC frame, approximately 5 terminals may be accommodated simultaneously on the same OFDM symbol. In the case of not employing subband multiplexing, 5 OFDM symbols (where the amount of unused bits used to fill in each OFDM symbol is large) need to be allocated for rate control information for 5 terminals. In the case of subband multiplexing, the same rate control information can be transmitted within one OFDM symbol, which would result in an 80% savings.

The savings in using subband multiplexing are greater for some diversity transmission modes. For space-time transmit diversity (STTD) mode, two transmit antennas transmit a pair of modulation symbols (denoted as s) in two symbol periods₁And s₂). The first antenna transmits a vector in two symbol periodsThe second antenna transmits the vector in the same two symbol periodsThe unit of STTD transmission is actually two OFDM symbols. With subband multiplexing, the rate control information for 10 terminals may be transmitted in two OFDM symbols, which is significantly less than the 20 OFDM symbols that would be required if each terminal transmitted its rate control information on a separate pair of OFDM symbols.

The savings are greater for a diversity transmit mode using 4 antennas and transmitting units of 4 OFDM symbols. For this diversity transmission mode, 15 terminal subbands may be multiplexed into one 4-symbol period. The rate control information for these 15 terminals may be transmitted in 4 OFDM symbols via subband multiplexing, which is significantly less than the 60 OFDM symbols that would be required if each terminal were transmitting rate control information over a separate set of 4 OFDM symbols.

Fig. 8B is a diagram illustrating the savings in uplink rate control transmissions for different numbers of active terminals in an exemplary OFDM system. For this system, up to 12 terminals may be multiplexed together by subband multiplexing. Each terminal may be assigned 18 subbands, each subband capable of carrying 3 information bits. The 12 terminals can each transmit 108 information bits in the 18 subbands assigned to them in 2 symbol periods. This is much less than the 24 symbol periods required for 12 terminals when subband multiplexing is not employed. If there are 12 terminals, a 22 symbol savings can be achieved, which is approximately 6% for a 367 symbol MAC frame. If there are 24 terminals, a saving of 44 symbols can be achieved, which represents about 12% of the MAC frame. As shown in fig. 8B, the amount of saving increases approximately linearly with the number of terminals.

Fig. 8C is a diagram illustrating the amount of savings in subband multiplexing pilot signals, rate control, and acknowledgement information on the uplink. In plot 812, the pilot signals and rate control information for multiple terminals are subband multiplexed into the pilot signal segment and rate control segment, respectively. In this case, no acknowledgement information is considered. In plot 814, the pilot signals, rate control information, and acknowledgement information for multiple terminals are subband multiplexed into the pilot signal segment, rate control segment, and acknowledgement segment, respectively.

As can be seen from the graph of fig. 8C, the savings are approximately linearly increasing with the number of terminals being multiplexed. In addition, when more types of information are multiplexed, the amount of savings increases. It can be seen that subband multiplexing can greatly reduce the amount of overhead for pilot signals and signaling, thereby making more available resources conveniently available for data transmission.

System for controlling a power supply

Fig. 7 is a block diagram of an embodiment of an access point 110x and a terminal 120x capable of supporting uplink subband multiplexing. At access point 110x, traffic data is provided from a data source 708 to a TX data processor 710, which TX data processor 710 formats, codes, and interleaves the traffic data to provide coded data. The data rate and coding scheme depend on rate control and coding control, respectively, provided by controller 730.

An OFDM modulator 720 receives and processes the coded data and pilot symbols to provide a stream of OFDM symbols. The processing by OFDM modulator 720 includes: (1) modulating the encoded data to form modulation symbols; (2) multiplexing the pilot symbols and the modulation symbols; (3) transforming the modulation symbols and pilot symbols to obtain transformed symbols; (4) a cyclic prefix is appended to each transformed symbol to form a corresponding OFDM symbol.

A transmitter unit (TMTR)722 then receives and converts the stream of OFDM symbols into one or more analog signals and further conditions (e.g., amplifies, filters, and frequency upconverts) the analog signals to generate a downlink modulated signal suitable for transmission over the wireless channel. The modulated signal is then transmitted via antenna 724 to the terminals.

In terminal 120x, an antenna 752 receives the downlink modulated signal and provides it to a receiver unit (RCVR) 754. Receiver unit 754 conditions (e.g., filters, amplifies, and frequency downconverts) the received signal and digitizes the conditioned signal to provide samples.

OFDM demodulator 756 then removes the cyclic prefix appended to each OFDM symbol, transforms each received transformed symbol using an FFT, and demodulates the received modulated symbols to provide demodulated data. RX data processor 758 then decodes the demodulated data to recover the transmitted traffic data and provides it to a data sink 760. The processing by OFDM demodulator 756 and RX data processor 758 is complementary to the processing by OFDM modulator 720 and TX data processor 710, respectively, in access point 110 x.

As shown in fig. 7, OFDM demodulator 756 obtains channel estimates and provides them to a controller 770. RX data processor 758 provides the status of each received packet. Based on various types of information received from OFDM demodulator 756 and RX data processor 758, a particular rate for each transport channel may be determined or selected by controller 770. Uplink pilot signals and signaling information (e.g., rates for downlink data transmission, acknowledgements for received data packets, etc.) are provided by controller 770, processed by a TX data processor 782, modulated by an OFDM modulator 784, conditioned by a transmitter unit 786, and transmitted by an antenna 752 to access point 110 x. The uplink pilot signal and signaling information may be transmitted over the group of subbands assigned to terminal 120x for these types of transmissions.

In access point 110x, the uplink modulated signals from terminal 120x are received by antennas 724, conditioned by receiver units 742, demodulated by an OFDM demodulator 744, and processed by an RX data processor 746 to recover the pilot signals and signaling information transmitted by the terminal. The recovered signaling information is provided to a controller 730 for controlling the processing of the downlink data transmitted to the terminal. The rate on each transmission channel may be determined, for example, based on rate control information provided by the terminal, or channel estimates from the terminal. The received acknowledgement may be used to retransmit data packets received in error by the terminal. Controller 730 may also derive the enhanced channel frequency response for each terminal based on the uplink pilot signals transmitted on the assigned subbands, as described above.

Controllers 730 and 770 direct the operation at the access point and terminal, respectively. Memories 732 and 772 store program codes and data used by controllers 730 and 770, respectively.

The uplink pilot signal and signaling transmission techniques described herein may be implemented in various ways. For example, these techniques may be implemented in hardware, software, or a combination of hardware and software. For a hardware implementation, the components used to implement any one or a combination of these techniques may be implemented within one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.

For the case of a software implementation, the techniques may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit (e.g., memory unit 732 or 772 in fig. 7) and executed by a processor (e.g., controller 730 or 770). The memory unit may be implemented within the processor or external to the processor, in which case it can be coupled to the processor in a variety of ways known in the art.

Headings are included herein for reference and to assist in locating particular sections. These headings do not limit the scope of the concepts described therein under, as these concepts may have applicability in other sections throughout the entire specification.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. It will be appreciated by those skilled in the art that various modifications to these embodiments will be readily apparent, and the principles described herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (29)

1. A method of receiving a pilot signal on an uplink of a wireless communication system, comprising:

grouping a plurality of usable subbands suitable for data transmission into at least two disjoint groups of non-contiguous subbands;

assigning a first non-contiguous group of subbands in the at least two disjoint non-contiguous groups of subbands to a first terminal;

receiving a first pilot transmission from the first terminal on a subband in the first non-contiguous group of subbands;

assigning a second non-contiguous group of subbands in the at least two disjoint non-contiguous groups of subbands to a second terminal; and

receiving a second pilot transmission from the second terminal on a subband in the second non-contiguous group of subbands.

2. The method of claim 1, further comprising:

a channel estimate for the first terminal is obtained based on the first pilot transmission received on subbands in the first non-contiguous set of subbands, where the channel estimate covers at least one subband not included in the first non-contiguous set of subbands.

3. The method of claim 2, wherein the channel estimates for the first terminal cover the plurality of available subbands.

4. The method of claim 1, wherein each of the at least two disjoint groups of subbands includes a same number of subbands.

5. The method of claim 1, wherein each of the at least two disjoint groups of subbands comprises S subbands, where S is an integer greater than or equal to a number of taps for a channel impulse response for the uplink.

6. The method of claim 1, wherein the subbands in each of the at least two disjoint groups of subbands are uniformly distributed across the plurality of usable subbands.

7. The method of claim 1, wherein the transmit power used for the first pilot transmission for each subband in the first non-contiguous group of subbands is adjusted by an adjustment factor greater than one to be higher than an average transmit power per subband to be used when the first pilot transmission is transmitted on all subbands.

8. The method of claim 7, wherein the adjustment factor is equal to a number of usable subbands divided by a number of subbands in the first non-contiguous group of subbands.

9. The method of claim 7, wherein a multiple of the adjustment of the transmit power used for the first pilot transmission in each subband of the first non-contiguous group of subbands is based on a per MHz power constraint and a full transmit power constraint for a frequency band used by the wireless communication system.

10. The method of claim 1, further comprising:

controlling a transmit power of a first pilot transmission from the first terminal such that a received signal-to-noise ratio, SNR, of the first terminal remains at or below a predetermined threshold SNR.

11. The method of claim 1, wherein the subbands of the first non-contiguous group of subbands assigned to the first terminal are adjacent to subbands of at least one other group of subbands assigned to at least one other terminal.

12. The method of claim 1, wherein the wireless communication system is an orthogonal frequency division multiplexing, OFDM, communication system.

13. The method of claim 1, wherein the plurality of available subbands are orthogonal subbands formed by orthogonal frequency division multiplexing, OFDM.

14. A method of receiving pilot signals on an uplink of an orthogonal frequency division multiplexing, OFDM, communication system, comprising:

grouping a plurality of usable subbands suitable for data transmission into a plurality of disjoint groups of non-contiguous subbands, wherein each disjoint group of non-contiguous subbands in the plurality of disjoint groups of subbands includes the same number of subbands;

allocating one non-contiguous subband group of the plurality of disjoint non-contiguous subband groups to each of at least two terminals, wherein the at least two terminals are partitioned into at least two non-contiguous subband groups;

receiving pilot transmissions from the at least two terminals on the at least two non-contiguous groups of subbands.

15. The method of claim 14, further comprising:

a channel estimate is obtained for each of the at least two terminals based on the received pilot transmission, wherein the channel estimate for each of the at least two terminals covers the plurality of usable subbands.

16. A method of transmitting pilot signals on an uplink of a wireless communication system, comprising:

receiving a subband group assigned for use with a pilot signal on the uplink, wherein the subband group comprises a subset of a plurality of available subbands suitable for data transmission;

determining a transmit power for each subband in the set of subbands, wherein the transmit power for each subband is adjusted by an adjustment factor greater than one to be higher than an average transmit power per subband to be used when pilot transmission is sent on all subbands;

transmitting a pilot signal on a subband of the group of subbands at the determined transmit power.

17. A method of receiving signaling information on an uplink of a wireless communication system, comprising:

grouping a plurality of usable subbands suitable for data transmission into a plurality of disjoint groups of non-contiguous subbands;

allocating one non-contiguous subband group of the plurality of disjoint non-contiguous subband groups to each of at least two terminals, wherein the at least two terminals are partitioned into at least two non-contiguous subband groups;

receiving signaling transmissions from the at least two terminals on the at least two non-contiguous groups of subbands in the same time interval.

18. The method of claim 17, wherein the signaling transmission comprises:

rate control information for downlink data transmission.

19. The method of claim 17, wherein the signaling transmission comprises:

acknowledgement information of data received through downlink.

20. The method of claim 17, wherein the transmit power used for signaling transmissions from each terminal on each subband is adjusted by an adjustment factor greater than one to be higher than the average transmit power per subband to be used when signaling transmissions are sent on all subbands.

21. The method of claim 17, wherein each non-contiguous group of subbands in the plurality of disjoint non-contiguous groups of subbands includes a same number of subbands.

22. The method of claim 17, wherein each of the plurality of disjoint sets of non-contiguous subbands comprises a variable number of subbands.

23. The method of claim 17, wherein a different modulation scheme is selected for each of the plurality of disjoint non-contiguous groups of subbands.

24. An apparatus in a wireless communication system having a plurality of subbands, comprising:

means for grouping a plurality of usable subbands suitable for data transmission into at least two disjoint groups of non-contiguous subbands;

means for assigning a first non-contiguous group of subbands in the at least two disjoint non-contiguous groups of subbands to a terminal;

means for receiving a pilot transmission from the terminal on a subband of the first non-contiguous group of subbands.

25. The apparatus of claim 24, further comprising:

means for obtaining channel estimates for the terminal based on pilot transmissions received on subbands in the first non-contiguous set of subbands, wherein the channel estimates cover at least one subband not included in the first non-contiguous set of subbands.

26. An apparatus in a wireless communication system, comprising:

means for receiving a subband group assigned for uplink pilot transmission, wherein the subband group comprises a subset of a plurality of available subbands suitable for data transmission;

means for transmitting pilot signals on subbands in the subband group, wherein a transmit power used for pilot signals on each subband in the subband group is adjusted higher than an average transmit power per subband to be used when pilot transmission is sent on all subbands by an adjustment factor greater than one.

27. An access point in a wireless communication system, comprising:

a demodulator for receiving a pilot transmission from a terminal, wherein a plurality of disjoint sets of non-contiguous subbands are formed from a plurality of available subbands for data transmission, and the pilot transmission is received on a first disjoint set of subbands selected from the plurality of disjoint sets of non-contiguous subbands and allocated to the terminal;

a controller that obtains a channel estimate for the terminal based on the received pilot transmission, wherein the channel estimate covers at least one subband not included in the first set of non-contiguous subbands assigned to the terminal.

28. The access point of claim 27 wherein the access point,

wherein the demodulator is further configured to receive a pilot transmission from a second terminal on a second non-contiguous set of subbands,

wherein the second non-contiguous set of subbands is selected from the plurality of disjoint non-contiguous sets of subbands and allocated to the second terminal.

29. An access point in a wireless communication system, comprising:

a demodulator for receiving signaling transmissions from at least two terminals in a same time interval, wherein a plurality of disjoint sets of non-contiguous subbands are formed by a plurality of usable subbands suitable for data transmission; wherein each of the at least two terminals is assigned to one of the plurality of disjoint non-contiguous subband groups; wherein at least two non-contiguous groups of subbands are assigned to the at least two terminals; wherein signaling transmissions from the at least two terminals are received on the at least two non-contiguous groups of subbands;

a controller for processing signaling transmissions received from the at least two terminals.