HK1073951B - Method and apparatus for selecting a transmit format for a transmission to a remote station - Google Patents

Description

Method and apparatus for selecting a transmission format for transmission to a remote station

Technical Field

The present invention relates generally to communications, and more particularly to a system for selecting an optimal transmission format, either for a single user or for multiple users of a synchronous transmission.

Background

The field of wireless communications has many applications including, for example, cordless telephones, wireless paging, wireless local loops, Personal Digital Assistants (PDAs), internet telephony, and satellite communication systems. One particularly important application is cellular telephone systems for mobile subscribers. As used herein, the term "cellular" system encompasses both cellular and Personal Communication Services (PCS) frequencies. Various air interfaces have been developed for such cellular telephone systems including, for example, Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA). In connection with them, various national and international guidelines have been established including, for example, Advanced Mobile Phone Service (AMPS), global system for mobile positioning (GSM), and interim guidelines 95 (IS-95). IS-95 and its derivatives IS-95A, IS-95B, ANSIJ-STD-008 (often collectively referred to herein as IS-95), as well as proposed high data rate systems, are published by the Telecommunications Industry Association (TIA) and other well-known body of guidelines.

A mobile telephone system configured pursuant to the use of the IS-95 standard employs CDMA signal processing techniques to provide efficient and robust mobile telephone service. Exemplary mobile telephone systems configured substantially in accordance with the use of IS-95 guidelines are described in U.S. patent nos. 5103459 and 4901307, which are assigned to the assignee of the present invention and incorporated herein by reference. An exemplary system using CDMA techniques is the CDMA2000ITU-R Radio Transmission Technology (RTT) candidate proposal, referred to herein as CDMA2000, issued by the TIA. The guidelines for cdma2000 are given in the draft version of IS-2000 and have been passed by the TIA. Another CDMA guideline is the W-CDMA guideline, which is incorporated in3rd Generation Partnership Project“3GPP”In (2), the file numbers are 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214.

The telecommunication criteria cited above are just some examples of various communication systems that can be implemented. However, there are problems in both of them. That is, multiple users must share limited system resources. In accordance with practical system implementations, resources such as frequency bandwidth, time, transmission power, or spreading code allocation are typically shared by multiple users within the system. When allocating these system resources, service providers must consider fairness and efficiency issues. In FDMA systems, the system bandwidth is divided into multiple frequency channels and each frequency channel is assigned to one user. In a TDMA system, the system bandwidth is divided into a plurality of time slots, and each time slot is assigned to a user. In a CDMA system, the system bandwidth is shared simultaneously by all users using spreading codes, where each user is assigned to one spreading code.

In systems that can transmit data traffic in packet format, such as TDMA and CDMA systems, efficient scheduling of multiple users is a key aspect of system performance. In conventional TDMA systems, only one user may be scheduled in one time slot. A slot is a time unit in which a predetermined number of bits are transmitted. The size of the time slot may vary according to system design constraints. Scheduling of data for transmission in time slots is typically based on whether the data is assigned to a user or whether the channel quality is within acceptable parameters. However, this scheduling method is not sufficient for optimizing system performance for several reasons.

The inefficiency associated with this scheduling method can occur when the amount of data allocated to a user is less than the data transfer capacity of the system at that time. If the channel quality is very high, a large number of data bits may be transmitted in the allocated time slot. However, if the actual data transmitted is less than the potential data capacity, then a "wide pipe" will be inefficient in terms of system throughput. It should be noted that the system throughput may be determined by the rate at which the initial information bits are actually received, which is different from the bit rate transmitted in the slotted channel. The information bits are encoded, interleaved, and modulated prior to transmission so that the number of transmission bits actually transmitted through the channel varies much from the initial number of information bits.

Another inefficiency problem is due to quantization loss. To simplify the implementation of the communication system and to reduce the signaling overhead, various parameters are quantized to a finite number of quantization levels. For example, the number of payload bits transmitted by a packet, the modulation format, and the frame duration are all parameters that are typically rounded to the allowed quantization levels. Due to the quantized nature of the transmission format, there is always a difference between the number of messages actually transmitted in a time slot and the number of bits that the system supports if not quantized. For example, if the system has data rates of 9.6kbps and 192kbps, the system may transmit at only one of the two rates. It is assumed that a channel for one user can support 15 kbps. However, to ensure success, the system allocates a transmission rate of 9.6kbps due to the quantization of the data transmission rate. Therefore, there is a loss of 5.4 kbps.

The embodiments described herein address the inefficiency problem described above by allowing the system to schedule multiple users within a transmission time slot rather than having only one user per time slot as in typical TDMA systems. By using CDMA techniques on a TDMA time slot structure, multiple users are scheduled to occupy a "wide channel" to optimize system throughput. The present embodiment will describe an apparatus for selecting a transmission format for each of multiple users arranged within one slot of a combined TDMA/CDMA system.

Disclosure of Invention

The method and apparatus presented herein are intended to meet the above-mentioned needs. In one aspect, a method for transmitting data from a base station to at least one remote station is provided, the method comprising: determining a priority for each of the at least one remote station; determining whether a number of walsh codes used by a plurality of possible transmission formats is less than a first predetermined amount; determining whether a total minimum power required for transmission is less than a second predetermined amount; determining whether a data payload of each of a plurality of possible transmission formats is less than an allocated amount; determining whether a frame duration of each of a plurality of possible transmission formats is equal; indicating that the plurality of possible transport formats are supported by the base station if the number of walsh codes is less than a first predetermined amount, the total minimum power required for transmission is less than a second predetermined amount, the data payload of each of the plurality of possible transport formats is less than the allocated amount, and the frame duration of each of the plurality of possible transport formats is equal; determining at least one transmission format using the priority of each of the at least one remote station; formatting the data payload into a message frame according to the selected transmission format, wherein the selected transmission format is selected from at least one transmission frame; and sending the message frame to the remote station.

In another aspect, a method for selecting a transmission format for a plurality of simultaneous transmissions from a base station, wherein each of the plurality of simultaneous transmissions is directed to a different remote station, the method comprising: determining that a plurality of possible transmission formats are supported by the base station, comprising: determining whether a number of walsh codes used by the plurality of possible transmission formats is less than a first predetermined amount, determining whether a total minimum power required for transmission is less than a second predetermined amount, determining whether a data payload of each of the plurality of possible transmission formats is less than an allocated amount, determining whether a frame duration of each of the plurality of possible transmission formats is equal, indicating that the plurality of possible transmission formats are supported by the base station if the number of walsh codes is less than the first predetermined amount, the total minimum power required for transmission is less than the second predetermined amount, the data payload of each of the plurality of possible transmission formats is less than the allocated amount, and the frame duration of each of the plurality of possible transmission formats is equal; extracting a plurality of transmission parameters from a plurality of possible transmission formats; determining a priority for each remote station; using the priority of each remote station within a revenue function; inserting a plurality of transmission parameters and priority information into a revenue function; and selecting a transmission format for each of the plurality of simultaneous transmissions based on the plurality of transmit parameters that maximize the revenue function.

In another aspect, an apparatus for transmitting data from a base station to at least one remote station is provided, the apparatus comprising: a memory element; and a processor configured to execute a set of instructions stored in the memory element, the set of instructions being: determining a priority for each of the at least one remote station; determining whether a number of walsh codes used by a plurality of possible transmission formats is less than a first predetermined amount; determining whether a total minimum power required for transmission is less than a second predetermined amount; determining whether a data payload of each of a plurality of possible transmission formats is less than an allocated amount; determining whether a frame duration of each of a plurality of possible transmission formats is equal; indicating that the plurality of possible transport formats are supported by the base station if the number of walsh codes is less than a first predetermined amount, the total minimum power required for transmission is less than a second predetermined amount, the data payload of each of the plurality of possible transport formats is less than the allocated amount, and the frame duration of each of the plurality of possible transport formats is equal; determining at least one transmission format using the priority of each of the at least one remote station; formatting the data payload as a message frame according to a selected transmission format, wherein the selected transmission format is selected from at least one transmission frame; and sending the message frame to the remote station.

In another aspect, an infrastructure element for selecting a transmission format for a plurality of simultaneous transmissions to different remote stations is presented, the infrastructure element comprising: apparatus for determining that a plurality of possible transmission formats are supported by a base station, the apparatus comprising: means for determining whether a number of walsh codes used by a plurality of possible transmission formats is less than a first predetermined amount, means for determining whether a total minimum power required for transmission is less than a second predetermined amount, means for determining whether a data payload of each of the plurality of possible transmission formats is less than an allocated amount, means for determining whether a frame duration of each of the plurality of possible transmission formats is equal, means for indicating that the plurality of possible transmission formats are supported by the base station if the number of walsh codes is less than the first predetermined amount, the total minimum power required for transmission is less than the second predetermined amount, the data payload of each of the plurality of possible transmission formats is less than the allocated amount, and the frame duration of each of the plurality of possible transmission formats is equal; means for extracting a plurality of transmission parameters from a plurality of possible transmission formats; means for determining a priority for each remote station; means for using the priority of each remote station within a revenue function; means for inserting a plurality of transmission parameters and priority information into a revenue function; and means for selecting a transmission format for each of the plurality of simultaneous transmissions based on the plurality of transmit parameters that maximize the revenue function.

In another aspect, an apparatus for determining an optimal transmission format for data transmitted from a base station to at least one remote station is presented, the apparatus comprising: means for determining a priority for each of the at least one remote station; means for determining whether a number of walsh codes used by a plurality of possible transmission formats is less than a first predetermined amount; means for determining whether a total minimum power required for transmission is less than a second predetermined amount; means for determining whether a data payload of each of a plurality of possible transmission formats is less than an allocated amount; means for determining whether a frame duration of each of a plurality of possible transmission formats is equal; means for indicating that the plurality of possible transport formats are supported by the base station if the number of walsh codes is less than a first predetermined amount, the total minimum power required for transmission is less than a second predetermined amount, the data payload of each of the plurality of possible transport formats is less than the allocated amount, and the frame duration of each of the plurality of possible transport formats is equal; means for determining at least one transmission format using the priority of each of the at least one remote station; means for formatting the data payload into message frames according to a selected transmission format, wherein the selected transmission format is selected from at least one transmission frame; and means for transmitting the message frame to the remote station.

Drawings

FIG. 1 is a diagram of a wireless communication network;

fig. 2 is a flow chart depicting a method for determining a transmission format for a plurality of simultaneous transmissions to a plurality of remote stations.

Fig. 3 is a flow chart illustrating the selection of an optimal transmission format from among the possible transmission formats for a remote station.

Fig. 4 is a flow chart illustrating the selection of the optimal transmission format for at least two remote stations.

Detailed Description

As illustrated in fig. 1, a wireless communication network 10 generally includes a plurality of mobile stations (also referred to as subscriber units or user equipment) 12a-12d, a plurality of base stations (also referred to as Base Transceiver Stations (BTSs) or node bs) 14a-14c, a Base Station Controller (BSC) (also referred to as a radio network controller or packet control function 16), a Mobile Switching Center (MSC) or switch 18, a Packet Data Serving Node (PDSN) or internetworking function (IWF)20, a Public Switched Telephone Network (PSTN)22 (typically a telephone company), and an Internet Protocol (IP) network 24 (typically the internet) four mobile stations 12a-12d, three base stations 14a-14c, one BSC16, one MSC18, and one PDSN20 are shown for clarity of illustration. Those skilled in the art will appreciate that there may be any number of mobile stations 12, base stations 14, BSCs 16, MSCs 18, and PDSNs 20.

In one embodiment, the wireless communication network 10 is a packet data service network. The mobile stations 12a-12d may be one of several different types of wireless communication devices such as a portable telephone that is connected to a laptop computer running an IP-based Web browser application, a cellular telephone with an associated hands-free car kit, a Personal Data Assistant (PDA) running an IP-based Web browser application, a wireless communication module included with a portable computer, or a fixed local communication module such as may be found in a wireless local loop or meter reading system. In the most general embodiment, the mobile station may be any type of communication unit.

The mobile stations 12a-12d may advantageously be configured to execute one or more wireless packet data protocols such as described in detail in, for example, the EIA/TIA/IS-707 guidelines. In a particular embodiment, the mobile stations 12a-12d generate IP packets destined for the IP network 24 and encapsulate these IOP packets into frames using a Point-to-Point protocol (PPP).

In one embodiment, the IP network 24 is coupled to a PDSN20, the PDAN20 is coupled to a MSC18, the MSC is coupled to a BSC16 and a PSTN22, and the BSC16 is coupled to the base stations 14a-14c, these couplings being accomplished over a wireline network configured for the transmission of voice and data packets in accordance with any of several known protocols, including, for example: e1, T1, Asynchronous Transfer Mode (ATM), IP, PPP, frame delay, HDSL, ADSL, or xDSL. In an alternative embodiment, the BSC16 is coupled directly to the PDSN20, and the MSC18 is not coupled to the PDSN 20.

In the normal operation of the wireless communication network 10, the base stations 14a-14c receive and demodulate sets of reverse signals from various mobile stations 12a-12d engaged in telephone calls, Web browsing, or other data communications. Each reverse signal received by a given base station 14a-14c is processed within the base station 14a-14 c. Each base station 14a-14c may communicate with a plurality of mobile stations 12a-12d by modulating and transmitting sets of forward signals to the mobile stations 12a-12 d. For example, as shown in fig. 1, the base station 14a communicates with first and second mobile stations 12a, 12b simultaneously, and the base station 14c communicates with third and fourth mobile stations 12c, 12d simultaneously. The resulting packets are forwarded to the BSC16, which BSC16 provides call resource allocation and mobility management functions, including soft handoff control of a call for a mobile station 12a-12d from one base station 14a-14c to another base station 14a-14 c. For example, the base station 12c communicates with two base stations 14b, 14c simultaneously. Finally, when the mobile station 12c moves far enough away from the base station 14c, the call will be handed off to the other base station 14 b.

If the transmission is a traditional telephone call, the BSC16 routes the received data to the MSC18, and the MSC18 provides additional routing services for the interface to the PSTN 22. If the transmission is a packet-based transmission, such as a data call destined for the IP network 24, the MSC18 routes the data packet to the PDSN20, and the PDSN20 will send the packet to the IP network 24. Alternatively, the BSC16 routes the packets directly to the PDSN20, and the PDSN20 sends the packets to the IP network 24.

In some communication systems, packets carrying data traffic are divided into subgroups, which occupy time slots of a transmission channel. For ease of explanation only, the nomenclature of a cdma2000 system is used herein. Such use is not intended to limit the application of the embodiments herein to cdma2000 systems. Embodiments may be implemented in other systems, such as WCDMA, without affecting the scope of the embodiments described herein.

In a cdma2000 system, the slot size is specified as 1.25ms duration. Moreover, the data traffic may be sent in message frames, which may vary in duration, e.g., 1.25ms, 2.5ms, 5ms, 10ms, 20ms, 40ms, or 80 ms. The terms "time slot" and "frame" are terms used in relation to different data channels within the same CDMA system or between different CDMA systems. A CDMA system includes many channels on the forward and reverse links, some of which are structurally different from others. Thus, the terms describing some channels differ according to the channel structure. For exemplary purposes only, the term "time slot" is used hereinafter to describe a packet of signals propagating through the air.

The forward link from a base station to a remote station operating within range of the base station can include multiple channels. Some forward link channels may include, but are not limited to, a pilot channel, a synchronization channel, a paging channel, a quick paging channel, a broadcast channel, a power control channel, an assignment channel, a control channel, a dedicated control channel, a Medium Access Control (MAC) channel, a fundamental channel, a supplemental code channel, and a packet data channel. The reverse link from the remote station to the base station also includes multiple channels. Each channel transmits different types of information to the destination. Typically, voice traffic is transmitted on the fundamental channel and data traffic is transmitted on the supplemental channel or the packet data channel. The supplemental channels are typically dedicated channels, while the packet data channels typically carry signals that are assigned to different users in a time multiplexed manner. Alternatively, the packet data channel is also described as a shared supplemental channel. For the purposes of describing the embodiments herein, the supplemental channel and the packet data channel are generally referred to as the data traffic channel.

Typically, a system scheduling algorithm is applied to determine data priority to a plurality of remote mobile stations when a scheduler unit or other infrastructure element within a base station receives data transmissions to the plurality of remote stations. The remote station with the highest priority is scheduled to transmit first in the system in which the remote stations are multiplexed in a TDMA fashion. After the remote station with the highest priority is transmitted, the TDMA type system will update the attributes of all remaining remote stations to determine which of the remaining has the highest priority next. Thus, a TDMA type system uses only the highest priority index and does not handle others. However, as described above, this scheduling method is not optimal because it is inefficient to transmit data to only one remote station over the entire time slot.

The embodiments described herein are directed to applying an optimal scheduling algorithm in which multiple users may be scheduled for transmission during an allocated time. In particular, embodiments are directed to systems that select multiple transmission formats for data packets so that data transmission to multiple users can be accomplished over a single time slot.

In one embodiment, the priority information and channel state information associated with each target remote station is used to determine the data transmission format for each target remote station. The priority information is typically determined by the scheduling unit or another infrastructure element within the base station.

In another embodiment, determining the data transmission format for each target remote station is based on selecting a transmission format that maximizes a revenue function. Suitable revenue functions are described below.

In another embodiment, the data transmission format selected for each target remote station is based on a maximized revenue function, and is also based on an effective transmission power and an effective spreading code.

Fig. 2 depicts a process for selecting a transmission format for a plurality of simultaneous transmissions from a base station to a plurality of remote stations during an assigned time duration. The selection procedure may be implemented within the base station by additional processing elements and memory elements, or the selection procedure may be introduced into already existing processing elements and memory elements within the base station. A number of other infrastructure elements may also play a role in implementing the above steps. At step 200, a base station receives a plurality of data traffic messages distributed to different remote stations operating within range of the base station. At step 202, a scheduling unit or other infrastructure element within a base station selects L candidate remote stations for receiving a transmission. The L best candidate remote stations are called U₁、U₂… … and U_L. In determining the L best candidate remote stations, the base station will assign a priority symbol P₁、P₂… … and P_LIs assigned to U₁、U₂… … and U_LIn which P is₁≥P₂≥……≥P_L. Each candidate remote station U₁、U₂、……And U_LAre respectively a data payload N₁、N₂… … and N_LWherein the payload may be determined based on the amount of information bits that occur to each remote station.

It should be noted that some communication systems have the ability to collect channel state information, such as carrier-to-interference ratio (C/I), from remote stations. The remote station uses a priori information of the pilot channel to determine the characteristics of the transmission medium. Embodiments disclosed herein may use this channel state information C/I to select the optimal transmission format for each remote station. Suppose (C/I)₁、(C/I)₂… …, and (C/I)_LChannel station information reported for all candidate remote stations.

Predetermined transmission format F₀、F₁、F₂… …, and F_M-1Is stored in the base station, wherein each transmission format F_iCorresponding to any or all combinations of the following transmission parameters: the modulation scheme used by the system, the number of orthogonal or quasi-orthogonal codes, the data payload size in bits, the duration of the message frame, and/or details regarding the encoding scheme. Some examples of modulation schemes used within communication systems are the quadrature phase shift keying scheme (QPSK), the eight phase shift keying scheme (8-PSK), and the sixteen-ary quadrature amplitude modulation (16-QAM). Some of the multiple coding schemes that can be selectively implemented are convolutional coding schemes, which can be implemented at different rates, or turbo coding, which includes multiple coding steps separated by interleaving steps.

Orthogonal and quasi-orthogonal codes, such as walsh codes, are used to channelize the information sent to each remote station. In other words, walsh codes are used on the forward link, allowing the system to cover multiple users each assigned a different orthogonal or quasi-orthogonal code on the same frequency for the same time duration.

Thus, the base station has the option to transmit data payloads in accordance with various transmission formats. For the purpose of illustration, the numbers that the base station has configured according to the transmission format are used hereThe payload is referred to as a frame. For this example, the term F₀Corresponding to an instance where no transmission is made to the remote station.

Once the base station determines the L best candidates and their associated attributes, the base station determines 210 each U_iSelecting a frame format f_iThus, a frame format set f₁、f₂… …, and f_LMaximize the revenue function J (). Examples of possible revenue functions are discussed in detail below.

In one embodiment, the base station is configured by collecting (f)_1-test、f_2-test… …, and f_L-test) Where a selection is performed by selecting a subset of the possible frame formats and then determining whether a certain condition is met. In one embodiment, the following four conditions are used:

1.

wherein Nb _ Walsh (F)_i) Is a transmission format F_iThe number of Walsh codes used in, Nb _ Walsh (F)₀) 0. The quantity "total available walsh codes for packet data" is a parameter that can be determined at the base station during the course of operation.

2.

Wherein E_i(F_K) Is using a transmission format F_KIs transmitted to U_iThe minimum power required. The amount "total available power for packet data" is a parameter that can be determined at the base station during the course of operation. It should be noted that this parameter is the remote station U_iIs also the transmission format F_KAs a function of (c).

3.Payload(f_i)≤N_iFor any i e {1, 2,. gtoreq., L },

where Payload is F in bits_iThe data payload of (1).

4.FrameDuaration(f_i)＝FrameDuaration(f_j) For any i, j e {1, 2_i≠F₀，f_j≠F₀，

Among them, FrameDuration (F)_i) Is to transmit a frame F_iThe frame duration specified within. It is worth noting that if for any i e {1, 2_i＝F₀Then fewer than L users are scheduled.

Once the base station selects the set of frame formats f that maximizes the revenue function J ()₁、f₂… …, and f_LThen, in step 220, the base station uses L frame formats f for the allocated time duration₁、f₂… …, and f_LAnd sending the message frame to L users.

Examples of revenue function J ()

The above-described embodiments for selecting a transmission format are based on using priority information applied to a revenue function. The revenue function may be any function that maximizes data throughput while ensuring a fair degree of allocation. "fairness" is a subjective quantity that depends on the requirements of the system provider. For example, a system provider may decide that over a longer period of time it is unacceptable for a single user to monopolize resources for large data transfers. However, the system provider may determine that over a shorter period of time a single user may accept exclusive resources. Fairness can also be specified by the arrival time of the data payload, or by the origin of the data payload, or by the amount of the data payload. Fairness can also be specified by quality of service or by the price of the communication access. These examples illustrate that "fairness" is a system constraint that can be defined in a very different way. However, the amount of "fairness" can be factored into various factors by appropriate revenue functions.

In one embodiment, the following revenue function J (), may be used:

where α ≧ 0 is a constraint that controls fairness.

Using the revenue function described above, if the data payload includes a large number of bits or the priority index is high, then the message frame will be scheduled.

In another embodiment, the following revenue function J (), may be used:

J(f₁，f₂，...f_L) 0, if f₁＝F₀

Others

Where α ≧ 0 is a constraint that controls fairness.

Using the revenue function described above, with highest priority P₁Is always scheduled to ensure fairness.

The transmission format selection process described in fig. 2 describes how to select a transmission format that maximizes a given revenue function. Other embodiments exist. Another multi-format f for how to select the best when multiple users are scheduled₁、f₂… …, and f_LEmbodiments of which are set forth herein. Another embodiment is described herein regarding how the best transmission format is selected if only one user is actually scheduled (except F0). These selections may also be analyzed to determine how many and which users are scheduled to maximize the revenue function J (), and the corresponding transmission format.

Fig. 3 depicts an embodiment on how the best transmission format is selected if only one user is scheduled. It includes the selection criteria of this example, where only one remote station is scheduled, but there are multiple transmission formats that satisfy the same revenue function.

In step 300, the base station selects a primary target U according to the priority index or the information bit in the buffer₁. In step 302, the base station selects at least one possible transmission format for transmission to the U₁The data traffic payload of. In one embodiment, the selection of the plurality of possible transmission formats is based on a revenue function that maximizes system throughput. At step 304, if there is more than one possible transmission format, then the program flow continues to step 306. If there are multiple transmission formats that maximize the revenue function J (), there is more than one possible transmission format. If only one possible transmission format is possible, the program flow continues to step 308 where the base station formats the data traffic payload in accordance with the selected transmission format.

In step 306, the base station selects an optimal transmission format according to the transmission format requiring the least walsh codes. In step 302, the base station formats the data traffic payload in accordance with the selected optimal transmission format.

Fig. 4 depicts another embodiment of selecting criteria when multiple remote stations need to be scheduled for transmission. The target remote station candidate is labeled V₁、V₂… …, and V_L. Wherein each V_iWith a priority index P_iIs related, thereby P₁≥P₂≥...≥P_L。

In step 400, the base station couples V₁Designated as the highest priority target remote station and set a variable V_iThe index of (c) is 2.

In step 402, the base station is the system supported V₁And V_iAll transmission formats are determined. The set of good transmit format pairs is denoted as { (f)_j，f_k): 1 ≦ j, k ≦ L, j ≠ k and L is the maximum number of remote stations that can be simultaneously scheduled }. In one embodiment, the base station estimates the frame duration, the number of walsh codes, and/or the required minimum transmit power associated with each transmit format to determine whether the system supports that transmit format.

In step 404, the base station determines (f) a pair of transmission frames for each determined in step 402_j，f_k) The amount of unused system resources such as walsh codes and transmission power remains.

In step 410, the base station estimates a given revenue function J () for each transmission format pair. The pair of transmission formats that maximizes the revenue function J () is selected as the best pair. At step 412, it is determined whether there are multiple transmit format pairs that maximize the revenue function. If there are more than one pair of transmitted frames that maximize the revenue function, the base station selects the pair of transmitted frames that require the fewest walsh codes at step 414. This program flow then continues to 420. If there is only one pair of transmitted frames that maximizes the revenue function, then program flow also continues to step 420.

In step 420, the base station determines V₁And V_iWhether the best transmit format pair is better than the previous best transmit format pair. In other words, the base station compares the best transmission frame pair determined during the period from the previous round to the current round of the best transmission format. The determination of the best transmission format pair to be compared therewith is to be compared with V₁The best candidate remote station scheduled together.

At step 430, index i is incremented and the above steps are repeated until all candidates are exhausted. When i reaches the last added value, the base station schedules V according to the determined optimal transmission format in step 440₁And V_bestThe synchronous transmission of (2).

Alternatively, the above process is rewritten using multiple loops, with the outer loop scanning each V_iMiddle loop scans each V₁The possible transmit formats, the inner loop, are candidates for scanning the second user using the remaining walsh codes and the remaining power. Those skilled in the art will appreciate that programming implementations may be varied without affecting the scope of the embodiments herein.

The above embodiments describe a search for the best transmission format for simultaneous transmission to two remote stations. However, the above embodiments may be extended to describe a search for an optimal transmission format for more than two remote stations. Except that only V is searched₁And V_iAll transmission formats, the base station can search from V₁To V_mWhere m is the number of simultaneous transmissions to m stations. Thus, in addition to estimating the transmit format pairs, the system estimates the set of transmit formats to maximize a given revenue function.

In another embodiment, a further step may be added to the system described herein to more fully utilize system resources. After the base station selects the best transmission format for multiple simultaneous transmissions, the base station determines whether any walsh codes and power remain unused. If there are unused Walsh codes and power, they are allocated in the remote station to be scheduled. This allocation may be on average or may be based on the priority index and/or minimum power requirements of the remote station. In one embodiment, the remaining walsh codes can be assigned based on the priority index of the remote station. In another embodiment, the remaining power is proportionally allocated according to the minimum power requirement.

As discussed previously, walsh codes or other orthogonal/quasi-orthogonal codes are important for providing transmission channelization to individual remote stations. An important aspect of using walsh codes is the relationship between the data bits used for covering and the transmission power level. The simplified explanation is that the error-controlled coding rate becomes lower and the transmission power efficiency is improved when more walsh codes are used to spread the original data bits.

Thus, another step that may be added to the above embodiment is to determine whether there is transmission power remaining unassigned at the base station. If there is remaining transmission power, the base station may follow the E of each remote station_i(f_K) Power is allocated proportionally in the data traffic payload.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with: a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination of devices designed to perform the functions described herein. A general purpose processor is preferably a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or other such configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. 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 (8)

1. A method for transmitting data from a base station to at least one remote station, comprising:

determining a priority for each of the at least one remote station;

determining at least one transmission format using the priority of each of the at least one remote station, the using the priority of each of the at least one remote station to determine the at least one transmission format comprising:

determining that a plurality of possible transmission formats are supported by the base station, wherein the determining comprises:

determining whether a number of walsh codes used by a plurality of possible transmission formats is less than a first predetermined amount;

determining whether a total minimum power required for transmission is less than a second predetermined amount;

determining whether a data payload of each of a plurality of possible transmission formats is less than an allocated amount;

determining whether a frame duration of each of a plurality of possible transmission formats is equal;

if the number of walsh codes is less than the first predetermined amount, the total minimum power required for transmission is less than a second predetermined amount, the data payload of each of the plurality of possible transport formats is less than the allocated amount, and the frame duration of each of the plurality of possible transport formats is equal, indicating that the plurality of possible transport formats are supported by the base station;

extracting a plurality of transmission parameters from a plurality of possible transmission formats;

inserting a plurality of transmission parameters and priority information into a revenue function; and

a maximized revenue function, wherein determining at least one transmission format is based on a plurality of transmission parameters of the maximized revenue function;

formatting the data payload into message frames according to the selected transmission format, wherein the selected transmission format is selected from at least one transmission frame; and

a message frame is sent to the remote station.

2. The method of claim 1, wherein the selected transmission format is selected from at least one transmission frame by selecting a transmission format that uses a fewest walsh codes.

3. The method of claim 1, wherein formatting the data payload into the message frame in accordance with the selected transmission format further comprises assigning an unused walsh code to the selected transmission format.

4. The method of claim 1, wherein transmitting the message frame to the remote station further comprises using an assigned minimum transmission power that is based on the selected transmission format and the remaining transmission power level.

5. An apparatus for determining an optimal transmission format for data transmitted from a base station to at least one remote station, comprising:

means for determining a priority for each of the at least one remote station;

means for using the priority of each of the at least one remote station to determine at least one transmission format, the means for using the priority of each of the at least one remote station to determine at least one transmission format further for:

determining that a plurality of possible transmission formats are supported by the base station, wherein the determining comprises:

means for determining whether a number of walsh codes used by a plurality of possible transmission formats is less than a first predetermined amount;

means for determining whether a total minimum power required for transmission is less than a second predetermined amount;

means for determining whether a data payload of each of a plurality of possible transmission formats is less than an allocated amount;

means for determining whether a frame duration of each of a plurality of possible transmission formats is equal;

means for indicating that the plurality of possible transport formats are supported by the base station if the number of walsh codes is less than a first predetermined amount, the total minimum power required for transmission is less than a second predetermined amount, the data payload of each of the plurality of possible transport formats is less than the allocated amount, and the frame duration of each of the plurality of possible transport formats is equal;

extracting a plurality of transmission parameters from a plurality of possible transport formats;

inserting a plurality of transmission parameters and priority information into a revenue function; and

a maximized revenue function, wherein determining at least one transmission format is based on a plurality of transmission parameters of the maximized revenue function;

means for formatting the data payload into message frames according to a selected transmission format, wherein the selected transmission format is selected from at least one transmission frame; and

means for transmitting the message frame to the remote station.

6. The apparatus of claim 5, further comprising: means for selecting a selected transmission format from at least one transmission frame by selecting the transmission format using the least walsh code.

7. The apparatus of claim 5, further comprising: unused walsh codes are assigned to the devices of the selected transmission format.

8. The apparatus of claim 5, further comprising: transmitting the message frame to the remote station further includes means for using the assigned minimum transmission power based on the selected transmission format and the remaining transmission power level.