RU2373666C2 - Pilot information transmission and signaling by upperlink in wireless communication systems - Google Patents

Abstract

FIELD: communication facilities.

SUBSTANCE: invention relates to communication engineering and can be used for providing of signalling at pilot information transmission by upperlink in wireless communication systems. For this at multiplexing of subranges, M used subranges in system is divided for Q non-intersecting group of subranges. Each group of subranges can be assigned to separate terminal for pilot information transmission by upperlink. Multitude of terminals can implement transmission simultaneously at assigned to it subranges. Power of pilot - signal transmission can be scaled with increasing for receiving of the same energy of pilot - signal, even if it is used S, instead of M subranges for pilot -signal transmission in each terminal. Pilot - signals transmission from terminals is received, and for each terminal it is introduced channel evaluation, on the basis of pilot - signal, accepted in assigned subranges. Channel evaluation contains response for additional subranges, not introduced into assigned group.

EFFECT: effectiveness increase of pilot -signal transmission and signalling by upperlink in system OFDM.

30 cl, 10 dwg

Description

RELATED PATENT APPLICATIONS

[0001] This patent application claims the priority of both provisional patent application US No. 60 / 422,368, filed October 29, 2002, entitled "Uplink Pilot and Signaling Transmission In Wireless Communication Systems", and provisional patent application US No. 60 / 422,362 , filed October 29, 2002, entitled "Channel Estimation for OFDM Communication Systems," which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

[0002] The present invention relates generally to data exchange, and more specifically to methods for transmitting pilot information and signaling information (eg, speed control) on an uplink in a wireless communication system.

BACKGROUND

[0003] Wireless communication systems are widespread and provide various types of communication, such as voice, packet data, and the like. Such systems may be multiple access systems configured to support communication with multiple users sequentially or simultaneously sharing available system resources. Examples of such multiple access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems and orthogonal frequency division multiple access (OFDMA) systems.

[0004] OFDM systems use orthogonal frequency division multiplexing (OFDM) to efficiently split the entire system bandwidth into a number of (N) orthogonal subbands. These subbands are also called tones, frequency bins, and frequency subchannels. Each subband can be considered as an independent transmission channel that can be used for data transmission.

[0005] In a wireless communication system, a modulated radio frequency (RF) signal from a transmitter can reach a receiver through a plurality of propagation paths. The characteristics of the distribution pathways usually change over time due to several factors. For OFDM systems, N subbands may have different channel states and may have different signal to noise ratio (SNR) values.

[0006] Typically, an accurate estimate of the response of the wireless channel between the transmitter and receiver is required for efficient data transmission over the available subbands. Channel estimation is usually performed by sending a pilot from the transmitter and measuring the pilot at the receiver. Since the pilot signal is composed of symbols that are known a priori to the receiver, the channel response can be estimated as the ratio of the received pilot symbols to the transmitted pilot symbols.

[0007] Pilot transmission refers to overhead in a wireless communication system. Therefore, it is desirable to minimize pilot transmission as much as possible. However, due to the presence of noise and other artifacts in the wireless channel, a significant amount of pilot transmission is necessary in order for the receiver to obtain a fairly accurate estimate of the channel response. In addition, due to the contributions of the propagation paths to the channel response, and because the propagation paths themselves usually change over time, the transmission of the pilot signal must be repeated. The length of time that a wireless channel can be considered relatively constant is often called the channel coherence time. To maintain high system performance, repetitive pilot transmissions should be located much closer than the channel coherence time.

[0008] In a downlink of a wireless communication system, one pilot transmission from an access point (or base station) can be used by several terminals to evaluate the response of individual channels from the access point to each of the terminals. For an uplink, a channel from each terminal to an access point typically requires estimation through separate pilot transmissions from each terminal.

[0010] Thus, in a wireless communication system, each of the plurality of terminals may require uplink pilot transmission to the access point. Moreover, uplink transmission of signaling information, such as rate control and acknowledgment information for downlink transmission, may be required. The uplink transmissions are performed using a time division multiplexing (TDM) method, a time slot can be assigned to each terminal, and then the terminal transmits its pilot signal and signaling information in the assigned time slot. Depending on the number of active terminals and the length of time slots for transmitting the pilot signal and signaling information, a relatively large proportion of the uplink transmission may be occupied. The indicated inefficiency in the uplink transmission of the pilot signal and signaling information is exacerbated in the OFDM system, where the data transmission capacity for the smallest transmission unit (usually one OFDM symbol) can be quite large.

[0011] Therefore, in the art there is a need for more efficient methods for transmitting pilot and signaling information in wireless communication systems (eg, OFDM systems).

SUMMARY OF THE INVENTION

[0012] The present description provides methods for more efficiently transmitting pilot signal and uplink signaling information in wireless communication systems. When multiplexing the subbands, the M usable subbands can be divided into Q disjoint groups of subbands, where each subband is included in only one group or is not included in any of the groups. Each group of subbands can then be assigned to a separate terminal. Many terminals can simultaneously transmit on their assigned subbands.

[0013] Using subband multiplexing, it is possible to accurately estimate the channel for each terminal over the entire usable band, based on pilot transmission on only a small subset of the usable subbands. If the total energy used for transmitting the pilot signal over S subbands is kept equal to that used otherwise for transmitting a pilot signal over all M used subbands, then in this case it is possible to transmit a pilot signal only over S subbands to accurately interpolate the channel response for other MS subbands.

[0014] One embodiment provides an uplink pilot transmission method in a multi-subband wireless communication system (eg, an OFDM system). According to this method, the M usable subbands suitable for transmitting data 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 evenly or unevenly distributed among the M usable subbands. Different groups of subbands are assigned to each of one or more terminals for transmitting uplink pilot signals. Then, the transmission of the pilot signal is received from one or more terminals on the assigned group of subbands. For each terminal, the pilot transmission power in each subband can be set higher (for example, by the Q factor), so that the same total pilot energy is used, even though the pilot is transmitted in S rather than in M subbands. The power scaling can be performed in such a way that the total transmit power available at each terminal will be known, the power limitations (for example, regulatory restrictions) are satisfied, and the cost of the hardware components will increase slightly (if at all). Then, a channel estimate for each terminal may be derived based on the pilot received on the subbands assigned to that terminal. The channel estimate for each terminal may cover one or more additional subbands not included in the group assigned to that terminal. For example, the channel estimate may include a response for all M usable subbands.

[0015] Subband multiplexing can also be used to transmit uplink signaling information. The signaling information may comprise rate control information used to transmit data in a downlink, acknowledgment for data received in a downlink, etc.

[0016] Various aspects and embodiments of the present invention are described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Distinctive features, the essence and advantages of the present invention will be more apparent from the following detailed description when considered in conjunction with the drawings, in which the same reference numbers indicate the same elements and in which:

[0018] FIG. 1 illustrates an OFDM system that supports multiple users;

[0019] FIGS. 2, 3, and 4 illustrate a frame structure, an OFDM subband structure, and an OFDM subband structure supporting subband multiplexing, respectively;

[0020] FIG. 5 illustrates an uplink pilot transmission process using subband multiplexing;

[0021] FIG. 6 illustrates a frame structure supporting subband multiplexing for pilot transmission and uplink signaling;

[0022] FIG. 7 is a block diagram of an access point and a terminal in an OFDM system; and

[0023] FIGS. 8A-8C show graphs of possible savings that can be obtained by multiplexing subbands when transmitting pilot and uplink signaling information.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The word "illustrative" is used in the present description to mean "serving as an example or illustration." An embodiment or design described herein as “illustrative” should not be construed as preferred or advantageous over other embodiments or designs.

[0025] The methods for transmitting a pilot signal and signaling information described herein can be used with various types of wireless communication systems. For example, these methods can be used in CDMA, TDMA, FDMA, and ODFM systems. These methods can also be used in hybrid systems, such as the OFDM TDM system, which transmits pilot / signaling and traffic data using time division multiplexing, whereby ODFMs are used for pilot transmission / signaling, and traffic data is used another transmission scheme. For clarity, these methods are described below for the case of an OFDM system.

[0026] FIG. 1 illustrates an OFDM system 100 supporting multiple users. OFDM system 100 includes multiple access points (ATs) 110 that communicate with multiple terminals (T) 120. For simplicity, only one access point is shown in FIG. An access point may also be called a base station or in some other way.

[0027] Terminals 120 may be distributed throughout the system. A terminal may also be called a mobile station, a remote station, an access terminal, or in some other way. Each terminal may be a fixed or mobile terminal capable of exchanging data with one or, possibly, multiple access points on the downlink and / or uplink at any given time. The downlink (or straight line) represents the transmission from the access point to the terminal, and the uplink (or reverse line) indicates the transmission from the terminal to the access point.

[0028] In FIG. 1, an access point 110 communicates with user terminals 120a-120f in a downlink and an uplink. Depending on the particular design of the OFDM system, an access point can communicate with multiple terminals simultaneously (e.g., across multiple subbands) or sequentially (e.g. across multiple time slots).

[0029] FIG. 2 illustrates the structure of a frame 200 that can be used in an OFDM system if a single frequency band is used for both the downlink and the uplink. In this case, the downlink and uplink can share the same frequency band using time division duplex (TDD).

[0030] As shown in FIG. 2, downlink and uplink transmissions occur in the MAC frame elements. Each MAC frame can be defined as covering a specific time interval. Each MAC frame is divided into a downlink phase 210 and an uplink phase 220. Downlink transmissions to multiple terminals can be multiplexed in the downlink phase using time division multiplexing (TDM). Similarly, uplink transmissions from multiple terminals can be multiplexed in the uplink phase using TDM. For the particular TDM implementation shown in FIG. 2, each phase is further divided into a plurality of time slots (or simply slots) 230. The slots may have a fixed or varying duration, and the duration of the slots may be the same or different for the phases of the uplink and downlink . For such a TDM implementation, each slot 230 in the uplink phase includes a pilot segment 232, a signaling segment 234, and a data segment 236. Segment 232 is used to transmit the pilot signal on the uplink from the terminal to the access point, segment 234 is used to transmit signaling (e.g., speed control, acknowledgment, etc.), and segment 236 is used to transmit data.

[0031] Slots in the uplink phase of each MAC frame may be assigned to one or more terminals for uplink transmission. Each terminal then transmits in its assigned slot (s).

[0032] The frame structure 200 represents a specific implementation that can be used in an OFDM system if only one frequency band is available. If two frequency bands are available, then downlink and uplink transmissions can be on separate frequency bands using frequency division duplex (FDD). In this case, the phase of the downlink can be implemented on one frequency band, and the phase of the uplink can be implemented on another frequency band.

[0033] The pilot and signaling methods described herein can be used for frames having a structure based on both TDD and FDD. For simplicity, these methods are described specifically for frames having a TDD-based structure.

[0034] FIG. 3 shows an OFDM subband structure 300 that can be used in an OFDM system. An OFDM system has a total bandwidth of W MHz that is divided into N orthogonal subbands using OFDM. Each subband has a bandwidth of W / N MHz. Of all N subbands, only M subbands are used for data transmission, with M <N. The remaining N-M subbands are not used and serve as guard bands allowing the OFDM system to satisfy the requirements for its spectral mask. M "usable" subbands include subbands from F to M + F-1.

[0035] For OFDM, data intended for transmission is first modulated (ie, symbol mapped) using a particular modulation scheme selected for use for a given subband. For N-M unused subbands, the signal value is set to zero. For each symbol period, M modulation symbols and N-M zeros for all N subbands are mapped to the time domain using the inverse fast Fourier transform (IFFT) to obtain mapped symbols that contain N samples in the time domain. The duration of each transformed symbol is inversely proportional to the bandwidth of each subband. For example, if the system bandwidth is W = 20 MHz and N = 256, then the bandwidth of each subband is 78.125 kHz, and the duration of each converted symbol is 12.8 μs.

[0036] OFDM can provide certain advantages, for example, the ability to counteract frequency selective fading, which is characterized by different channel gains at different frequencies of the full system bandwidth. It is well known that frequency selective fading causes intersymbol interference (ISI), which is a phenomenon in which each character in the received signal acts as a distortion for subsequent characters in the received signal. ISI distortion degrades performance, affecting the ability to correctly detect received characters. Frequency selective fading in OFDM is usually counteracted by repeating a portion (or an added cyclic prefix) of each transformed symbol when forming the corresponding OFDM symbol, which is then transmitted.

[0037] The length of the cyclic prefix (ie, the number of repetitions) for each OFDM symbol depends on the delay spread in the channel. The delay spread for a given transmitter is the difference between the moments of the earliest and latest arrival of the signal at the receiver for the signal transmitted by that transmitter. The delay spread for the system is the worst-expected delay spread case for all terminals in the system. To effectively counter ISI, the cyclic prefix must have a length greater than the delay spread.

[0038] Each converted symbol has a duration of N sample periods, with each sample period having a duration of (1 / W) μs. The cyclic prefix can be defined as containing Cp samples, where Cp is an integer that is greater than or equal to the number of taps (L) for the impulse response of the wireless channel (i.e., Cp≥L). In this case, each OFDM symbol includes N + Cp samples and each symbol period lasts N + Cp sample periods.

PASSENGER TRANSMISSION ON THE Ascending Line

[0039] In some OFDM systems, pilot signals are transmitted on the uplink by the terminals to enable the access point to perform the uplink channel estimation. If the TDD-TDM frame structure shown in FIG. 2 is used, then each terminal can transmit its pilot on the uplink in the pilot segment of its assigned slot. Typically, each terminal transmits a pilot on the uplink on all M usable subbands at full transmit power. This enables the access point to estimate the uplink response for the entire band used. Although such an uplink pilot transmission scheme is effective, it is also not effective since a relatively large proportion of the uplink phase can be used to transmit pilot signals by all active terminals. The pilot segments for all active terminals may comprise a significant portion of the uplink phase.

[0040] The present description provides methods for more efficient uplink pilot transmission in an OFDM system. In order to be effective, the pilot transmission scheme must be designed such that accurate channel estimates can be obtained for each active terminal based on the uplink pilot transmission for that terminal. However, it was found that the quality of the channel estimates is generally determined by the total energy of the pilot signal, and not by the features of the pilot transmission scheme. The total pilot energy is equal to the transmit power used for the pilot multiplied by the duration of the pilot transmission.

[0041] An accurate channel estimate can be obtained for the entire band used, based on pilot transmission only in S subbands, where S is selected so that Cp≤S≤M and is usually much less than M. One such channel estimation method is described in the aforementioned provisional application for US patent No. 60/422,638, provisional application for US patent No. 60/422,632 and provisional application for US patent [patent attorney index No. 020718]. In fact, it can be shown that if the total energy used to transmit a pilot signal in S subbands is equal to the total energy used to transmit a pilot signal in all M subbands, then exact channel response interpolation for other MS subbands is possible based on the pilot transmission -signals in S subbands using the channel estimation methods mentioned above. In other words, for the same total pilot energy, the interpolated channel response for the M-S subbands usually has the same quality (for example, the average root mean square error) as the channel estimate based on pilot transmission on all M subbands.

[0042] To enable simultaneous uplink pilot transmission for multiple terminals, subband multiplexing may be used. To implement multiplexing of the subbands, the M usable subbands can be divided into Q disjoint groups of subbands such that each usable subband is included in only one group or is not included in any of the groups. Q groups can include the same or different number of subbands, and the subbands in each group can be distributed evenly or unevenly across the M used subbands. It is also not mandatory to use all M subbands in Q groups (i.e., some of the usable subbands may not be used for pilot transmission).

и

, где "

" обозначает оператор получения наименьшего целого. Количество поддиапазонов в каждой группе должно быть равным или большим разбросу задержек таким образом, что уменьшаются эффекты ISI и может быть получена более точная оценка канала.[0043] In one embodiment, each group includes S subbands, wherein

and

where "

"denotes the operator of obtaining the smallest integer. The number of subbands in each group should be equal to or greater than the delay spread in such a way that the ISI effects are reduced and a more accurate channel estimate can be obtained.

[0044] FIG. 4 shows an embodiment of an OFDM pilot structure 400 that can be used in an OFDM system and which supports subband multiplexing. In this embodiment, the M usable subbands are initially divided into S disjoint sets, each set including Q continuously consecutive subbands. Q subbands in each set are assigned to Q groups so that the i-th subband in each set is assigned to the i-th group. In this case, the S subbands in each group will be evenly distributed over the M usable subbands so that successive subbands in the group are separated by Q subbands. M subbands can be distributed into Q groups in any other way that is within the scope of the present invention.

[0045] Q groups of subbands may be assigned to no more than Q terminals for pilot transmission on the uplink. Moreover, each terminal transmits a pilot signal in its assigned subbands. When multiplexing the subbands, no more than Q terminals can simultaneously transmit pilot signals on the uplink of no more than M usable subbands. This can significantly reduce the time required to transmit the pilot signal on the uplink.

[0046] In order to provide the access point with the possibility of obtaining high quality channel estimates, each terminal can increase the transmit power per subband by a factor of Q. This leads to the fact that the total pilot energy for transmitting the pilot signal to S assigned subbands will be same as when all M subbands are used for pilot transmission. The same total pilot energy allows the access point to estimate the channel response over the entire usable band based on a set of M usable subbands with little or no loss in quality, as described below.

[0047] An OFDM system may operate in a frequency band having a power limit per MHz of P dB · mW / MHz and a total power limit of P · W dB · mW. For example. The 5 GHz UNII band includes three 20 MHz frequency bands designated UNII-1, UNII-2 and UNII-3. These three frequency bands have limitations on the total transmit power of 17, 24 and 30 dB · mW and power limits on the MHz of 4, 11 and 17 dB · mW / MHz, respectively. The terminal power limit can be selected based on the lowest power limit for the three frequency bands so that the power limit per MHz is 4 dBmW / MHz and the total power limit is P · W = 17 dBm mW.

[0048] Groups of subbands can be formed such that the total transmit power can be used to transmit the pilot on the uplink, even if restrictions on the total power and power per MHz are imposed on each terminal. In particular, if the distance between the subbands in each group is approximately 1 MHz, then each terminal can transmit the pilot signal on the uplink to S subbands assigned to it with a power of 1 subband of R dB · mW, and at the same time satisfy the restriction condition power per MHz. Moreover, the total transmission power S of the subbands is P · S dB · mW, which is approximately equal to P · W dB · mW, since S≈W due to the separation of 1 MHz. In the general case, the limitations of the total power and power per MHz can be satisfied by suitable scaling, provided that S> W, where W is given in units of MHz.

[0049] In the illustrative OFDM system, the system bandwidth is W = 20 MHz, N = 256, and M = 224. The OFDM pilot structure includes Q = 12 groups, with each group including S = 18 subbands. For such a pilot structure, 216 or 224 usable subbands can be used simultaneously for uplink pilot transmission, and the remaining 8 subbands are not used.

[0050] In general, the amount of transmit power that can be used in each subband in each group depends on various factors, such as (1) limiting the total power and power per MHz and (2) the allocation of subbands in each group. The terminals can transmit the pilot signal on the uplink with full power, even if the distance between the subbands is not uniform and / or does not exceed 1 MHz. The determined power values for use in the subbands are determined based on the distribution of the subbands in Q groups. For simplicity, suppose that the S subbands in each group are evenly distributed and separated by the required minimum interval (for example, at least 1 MHz).

[0051] FIG. 5 is a flowchart of an embodiment of a process 500 for transmitting an uplink pilot signal using subband multiplexing. First, the M usable subbands are divided into Q disjoint groups of subbands (step 512). This separation may be performed once, based on the expected load of the OFDM system. Alternatively, the M usable subbands may be dynamically shared when changes in system load require it. For example, fewer groups may form when the system load is small, and more groups may form during peak system loads. In any case, the separation is performed in such a way that the condition S≥Cp is satisfied for each group.

[0052] One group of subbands is assigned to each active terminal for pilot transmission on the uplink (block 514). Assignment of subbands may be performed during call setup or at a later point in time, and may be reported to the terminal in the form of signaling. After that, each terminal transmits a pilot signal on the uplink on its assigned subbands (step 522). Each terminal can also scale the transmit power used to transmit the pilot on the uplink, so that the amount of transmit power used for each subband is determined based on various factors mentioned above. The amount of transmit power for use in each subband (or each group of subbands) can also be determined by the access point and sent as signaling to the terminal along with the assignment of the subbands.

[0053] The access point receives uplink pilot transmissions from all active terminals on all or a subset of the M usable subbands (block 532). The access point then processes the received signal to obtain a channel estimate for each subband assigned to each active terminal (block 534). Then, for each active terminal, a channel estimate for the entire used band can be derived based on the channel estimate obtained for the assigned subbands (block 536). The channel estimate for the entire usable band can be derived from the channel estimate for a subset of the usable subbands using various methods. One such channel estimation method is described in the aforementioned US provisional patent application No. 60 / 422,638, US provisional patent application No. 60 / 422,362 and US provisional patent application [patent attorney index 020718]. The channel estimate for the entire usable band can also be derived by interpolating the channel estimate for each subband for a subset of the usable subbands.

[0054] For each active terminal, a channel estimate for the entire usable band can then be used to transmit data on the downlink and / or uplink to or from the terminal (block 538). Uplink pilot transmission and channel estimation is typically performed continuously during a communication session to obtain current channel estimates.

[0055] A model for an OFDM system may be expressed as:

where r is a vector with N elements for symbols received on N subbands;

x is a vector with N elements for symbols transmitted on N subbands (some elements may be zero);

H is an (N × 1) vector for the channel frequency response between the access point and the terminal;

n is the additive white Gaussian noise vector for N; and

“o” means the Hadamard product (ie, the dot product, where the ith element of r is the product of the ith elements of x and H ).

It is assumed that noise n has a zero mean and a variance of σ ² .

[0056] With subband multiplexing, each active terminal transmits a pilot on its assigned S subbands during the pilot transmission interval. The transmitted pilot for each terminal may be denoted as an (N × 1) vector x _i , which includes pilot symbols for each of the S assigned subbands, and zeros for all other subbands. The transmit power for the pilot symbol for each assigned subband can be expressed as P _UL = x ² _{i, j} , x _{i, j} is the pilot symbol transmitted in the jth subband by terminal i.

канала для каждого поддиапазона для терминала i может быть выражена как:[0057] Rating

channel for each subband for terminal i can be expressed as:

представляет собой (S×1) вектор a _i/ b _i=[a₁/b₁…a_s/b_s]^T, который включает в себя отношения для S поддиапазонов, назначенных терминалу i. Оценка

канала для каждого поддиапазона может быть выполнена точкой доступа для терминала i, основываясь на принятых и переданных символах пилот-сигнала для каждого из S поддиапазонов, назначенных терминалу. Оценка

канала для каждого поддиапазона, таким образом, отражает частотный отклик канала для терминала i для S назначенных поддиапазонов.Where

represents (S × 1) the vector a _i / b _i = [a ₁ / b ₁ ... a _s / b _s ] ^T , which includes the relationships for S subbands assigned to terminal i. Rating

the channel for each subband may be performed by an access point for terminal i, based on the received and transmitted pilot symbols for each of the S subbands assigned to the terminal. Rating

channel for each subband, thus, reflects the frequency response of the channel for terminal i for S assigned subbands.

канала для каждого поддиапазона. Используют несколько способов. Один такой способ, как указывалось выше, описан в вышеупомянутых предварительной заявке на патент США №60/422638, предварительной заявке на патент США №60/422362 и предварительной заявке на патент США [индекс патентного поверенного 020718].[0058] The estimate for H in equation (1) can be obtained from the estimate

channel for each subband. Use several ways. One such method, as mentioned above, is described in the aforementioned provisional application for US patent No. 60/422638, provisional application for US patent No. 60/422362 and provisional patent application US [patent attorney index 020718].

[0059] If all N subbands are used for data transmission (ie, M = N), it can be shown that the mean square error (MSE) for channel estimation obtained based on the transmission of the pilot signal over only S subbands using the methods described in the aforementioned provisional application for US patent No. 60/422,638, provisional application for US patent No. 60/422,362 and provisional application for US patent [patent attorney index 020718], is the same as the MSE for channel estimation obtained based on the pilot transmission -Signal on all N subband x if the following conditions are satisfied:

1. Choose S≥Cp and S≥W;

2. Uniform distribution of S subbands in each group over N subbands; and

3. Set the transmit power for each of the S assigned subbands to N / S higher than the average transmit power P _avg , defined below.

[0060] The total transmit power that can be used for transmission by the terminal is usually limited to a lower value: from (1) the _total transmit power P _total of the terminal (which may be limited by the terminal power amplifier) and (2) the P · W limit to full power for the working frequency band. The average transmit power P _avg is equal to the smallest of P _total / N and P · W / N. For example, P _avg = P · W / N if the total transmit power that can be used by the terminal is limited by regulatory constraints.

[0061] If only a subset of all N subbands (ie, M <N) is used for data transmission, which is the case if some subbands are used as guard bands, then the minimum mean square error (MMSE) is only achieved if S = M. However, it was found in the aforementioned provisional application for US patent No. 60/422,638, provisional application for US patent No. 60/422,362 and provisional application for US patent [patent attorney index 020718], that if S ≈ 1.1 CP, then the MSE is more close to MMSE. Hence, for the case S≤M <N, the MSE is minimized for channel estimation obtained on the basis of transmitting the pilot signal over only S subbands if the following conditions are satisfied:

1. Choose S ≈ 1.1 Cp and S> W;

2. Uniform distribution of S subbands in each group across M data subbands; and

3. Set the transmit power for each of the S assigned subbands to N / S higher than the average transmit power P _avg described above.

RISE ALARM TRANSMISSION

[0062] In many wireless systems, terminals may need to send uplink signaling information to an access point. For example, terminals may need to inform the access point of speed (s) for use in downlink data transmission, send acknowledgment for received data packets, etc. Signaling information usually contains a small amount of data, but it may be necessary to send them in a timely manner and possibly on a regular basis.

[0063] In some systems, there may be a need to send uplink speed control information to indicate a rate that can be used in the downlink for each one or more transmission channels. Each transmission channel can correspond to a spatial subchannel (i.e., eigenmode) in a system with multiple inputs and multiple outputs (MIMO), a subband or frequency subchannel in an OFDM system, a time slot in a TDD system, etc. Each terminal can estimate the downstream channel and determine the maximum speed that can be supported by each of the transmission channels. The rate control information for the transmission channels can then be sent back to the access point and used to determine the downlink data rate to the terminal. The speed control information may be in the form of one or more speed codes, each of which may be mapped to a specific combination of coding rate, modulation scheme, etc. Alternatively, the rate control information may be provided in some other form (for example, SNR at reception for each transmission channel). In any case, the rate control information for each transmission channel may contain from 3 to 4 bits, and the rate control information for all transmission channels may contain a total of 15 bits.

[0064] As another example, it may be necessary to communicate the channel response or frequency selectivity information to the access point. The number of bits required for a channel response or frequency selectivity information may depend on the degree of structuring of the information to be sent (for example, for each subband or for each Nth subband).

[0065] The present disclosure also provides methods for more efficiently transmitting uplink signaling information in an OFDM system. The M usable subbands can be divided into Q _R disjoint groups, with each usable subband present in only one group or not present in any of them. Q _R groups may include the same or different number of subbands. The grouping of the used subbands for uplink signaling information may be the same or different from the grouping of the used subbands for transmitting the pilot on the uplink. Each group of subbands can be allocated to one terminal for signaling on the uplink. Many terminals can transmit signaling information simultaneously on their assigned subbands.

[0066] Using subband multiplexing to send uplink signaling information can provide various benefits. Due to the relatively high capacity of the OFDM symbol, it may be extremely inefficient to allocate whole OFDM symbols by the active terminal if only a small amount of data needs to be transmitted. Using subband multiplexing, several subbands allocated to each active terminal can be commensurate with the amount of data that needs to be transmitted.

[0067] The savings provided by subband multiplexing can be even greater if transmit power per subband is increased by a plurality of terminals jointly multiplexed in one time slot. Higher transmit power per subband leads to higher SNR when received at the access point, which allows a higher order modulation scheme to be maintained. In turn, this makes it possible to transmit more data or information bits in each subband. Alternatively, fewer subbands may be assigned to each terminal so that more terminals can be jointly multiplexed in one time slot. Fewer subbands can provide the necessary capacity for data transmission if a higher order modulation scheme is used.

[0068] Subband multiplexing can also be used to transmit uplink acknowledgment. For some systems, it may be necessary to send acknowledgment by the receiver to confirm the correct or erroneous detection of each packet received by the receiver. Improving system performance can be achieved by reducing the structure of resource allocation for acknowledgment transmission (i.e., by assigning a group of subbands instead of an entire OFDM symbol to each terminal).

[0069] The amount of confirmation data sent may differ from terminal to terminal and also from frame to frame. This is the case, since each terminal usually sends acknowledgment only for packets received in the current / previous MAC frame, and the number of packets sent to each terminal may differ for different terminals and at different times. In contrast, the amount of data sent for speed control is usually more constant.

[0070] A plurality of schemes may be used to allocate subbands for uplink transmission of various types of signaling (eg, acknowledgment) for active terminals. In one design, M usable subbands are divided into Q _A disjoint groups. Q _A groups may include the same or different number of subbands. Each active terminal may be assigned a different number of subbands for transmission of acknowledgment. For this design, the number of subbands assigned to a given terminal may be proportional to the number of packets sent to the terminal.

[0071] In another design, each active terminal is assigned a fixed number of subbands for acknowledgment transmission. However, the modulation scheme used by each terminal is not fixed, but can be selected based on the state of the channel. For a bi-directional channel, where the downlink and uplink are highly correlated, the transmission capacities for the downlink and uplink are dependent. That is, if more packets can be sent on the downlink in a given time period due to a better channel condition, then the same channel state can support the transmission of more information bits on the uplink in a given time interval. Thus, by allocating a fixed number of subbands to each active terminal, but allowing modulation to be adapted based on the state of the channel, more acknowledgment bits can be transmitted if necessary.

[0072] To simplify the assignment of subbands to the active terminal, the subbands can be divided into groups, and groups of subbands can be assigned to the terminals, rather than separate subbands. In general, each group can include any number of subbands, depending on the degree of structure required, for assigning subbands. For example, 37 subband groups can be formed with each group including 6 subbands. Then this terminal can be assigned any number of groups of subbands depending on the data it needs.

[0073] For a specific OFDM system design, 150 to 2000 bits can be transmitted in two OFDM symbols in the speed range supported by the system. This range of transmission rates is also achieved provided that a higher transmission power is used for each subband with subband multiplexing. Each of the 37 groups of subbands for the example described above can be used to transmit from 150/37 to 2000/37 bits for confirmation, depending on the state of the channel. Thus, a fixed number of subbands in each group can transmit a different number of bits for confirmation, depending on the speed selected for use, which in turn depends on the state of the channel.

[0074] In certain situations, it may be necessary to maintain transmit power per subband at the same level as for data transmission. Such a situation may arise, for example, if all used subbands are allocated to one terminal. However, if the subbands have low data throughput, then the requirements for this are correspondingly lower. Two OFDM symbols may be sufficient for acknowledgment data for all proposed channel configurations.

[0075] In an alternative scheme, acknowledgment data is sent along with the uplink packet data. For acknowledgment data, a delay may be introduced if it is necessary to wait until the packet data is sent on the uplink. If an additional delay is permissible, confirmation data can be sent practically without additional overhead information, since the amount of confirmation data is usually small and usually corresponds to the equalization part of the data packet transmitted on the uplink.

[0076] In yet another design, acknowledgment data is sent along with rate control information. The group of subbands assigned to each active terminal for transmitting speed control may have more bandwidth than is necessary for transmitting speed control information. In this case, acknowledgment data may be sent using the excess bandwidth of the subbands assigned for speed control.

[0077] If subband multiplexing is used to transmit signaling information on the uplink, the access point can process the received signal, individually restoring the signaling (eg, speed control and acknowledgment) sent by each terminal.

ILLUSTRATIVE FRAME STRUCTURE WITH MULTIPLEXING OF SUB-RANGE

[0078] FIG. 6 illustrates an embodiment of a frame structure 600 with support for subband multiplexing for pilot transmission and uplink signaling. The MAC frame is divided into a downlink phase 610 and an uplink phase 620. The uplink phase is further divided into pilot segment 622, signaling segment 624, and multiple slots 630. Subband multiplexing can be used for segment 622 so that multiple terminals can simultaneously transmit pilot on the uplink in that segment. Similarly, subband multiplexing can be used for segment 624 such that multiple terminals can simultaneously transmit signaling (eg, speed control information, acknowledgment, etc.) on the uplink in that segment. Slots 630 may be used to transmit packet data, messages, and other information. Each slot 630 may be assigned with or without subband multiplexing to one or more active terminals. Each slot 630 can also be used to send service messages to multiple terminals.

[0079] Various other frame structures may also be designed to be used, which is within the scope of the present invention. For example, the uplink phase may include a rate control segment used to transmit rate control information and an acknowledgment segment used to transmit acknowledgment data. As another example, a frame can be divided into multiple phases of the uplink and downlink, and different phases can be used for various types of transmission, such as traffic data, pilot, speed control signaling, and acknowledgment.

OPTIONS FOR CARRYING OUT

[0080] Subband multiplexing can significantly reduce the amount of resources required for pilot transmission and uplink signaling, as shown in the calculations below. However, there may be a need to consider various factors when implementing subband multiplexing, for example, (1) overhead signaling for assigning subbands to a terminal, (2) time shifts between uplink transmissions received from the terminals, and (3) frequency shift between uplink transmissions from terminals. Each of these factors is described in more detail below.

ALARM SIGNALING

[0081] Service signaling is necessary to perform assignment of subbands to each terminal. For the pilot signal and rate control information, each terminal may be assigned a specific group of subbands for each or all types of uplink transmissions. This assignment can be made during call setup, and the assigned subbands do not usually require confirmation or change for each MAC frame.

[0082] In the case of 24 groups of subbands for no more than 24 terminals, 5 bits will be sufficient to identify the specific group of subbands assigned to the terminal. These 5 bits can be included in the control message transmitted to the terminal to bring it into an active state. If the control message is 80 bits long, then 5 bits for assigning subbands will increase the message length by approximately 6%.

[0083] The scope of the signaling will be greater if there is more flexibility in forming groups of subbands and / or if groups can be assigned dynamically by the terminal. For example, if the number of subbands assigned for transmission of acknowledgment can vary from frame to frame, then a larger amount of overhead signaling will be required to complete the assignment of the subbands.

TIMING OF THE RISING LINE

[0084] A plurality of terminals capable of simultaneously transmitting by multiplexing subbands can be located throughout the system. If these terminals have different distances to the access point, then the propagation times for the signals transmitted from these terminals will be different. In this case, if the terminals transmit their signals at the same time, the access point receives signals from these terminals at different points in time. The difference between the earliest and latest arrival times of the signals at the access point depends on the difference in round-trip delays for the terminals with respect to the access point.

[0085] The difference in arrival times for signals from different terminals may fall within the allowable delay spread interval for the most distant terminals. For example, for an access point with a coverage area of 50 m, the maximum difference in arrival times between the earliest and latest arrivals is approximately 330 nsec. This constitutes a significant portion of the cyclic prefix having a length of 800 nsec. Moreover, the effect of violating the acceptable range of delay spread is worse for terminals at the boundary of the coverage area, which most require resistance to delay spread due to multipath propagation.

[0086] In one embodiment, to account for the difference in round-trip delays for active terminals, the uplink timing for each active terminal is adjusted so that its signal arrives at the access point within a particular time window. A timing setting loop can be maintained for each active terminal and can estimate the round-trip delay for a given terminal. In this case, the uplink transmission from the terminal may be delayed or accelerated by an amount determined by estimating the round-trip delay so that the uplink transmissions from all active terminals arrive at the access point within a specific time window.

[0087] The timing setting for each active terminal may be inferred based on a pilot or some other uplink transmission from the terminal. For example, an uplink pilot may be correlated with a pilot copy of the access point. The correlation result is an indication of whether the received pilot signal is delayed or leading relative to the pilot signals from other terminals. Then, 1 bit of the timing setting value can be transmitted to the terminal to indicate a slowdown or acceleration of its timing by a specific value (for example, ± the period of one sample).

FREQUENCY OFFSET

[0088] If subband multiplexing is used to allow multiple terminals to simultaneously transmit in their assigned subbands, then signals from nearby terminals can cause significant interference to signals from remote terminals if all terminals are transmitting at full power. In particular, it can be shown that a frequency offset between the terminals can lead to crosstalk between the subbands. Such interference may cause deterioration of the channel estimate derived from the uplink pilot signals and / or increase the bit error rate of the uplink data transmission. To mitigate the effects of crosstalk between the subbands, terminal power control can be performed so that the near terminals do not cause excessive interference to the remote terminals.

[0089] The effect of interference from near terminals has been studied and it has been found that coarse power control can be applied to mitigate the effect of crosstalk between subbands. In particular, it was found that if the maximum frequency mitigation between the terminals is 300 Hz or less, then by limiting the SNR for nearby terminals to 40 dB or less, the loss for other terminals in the SNR will be 1 dB or less. If the frequency offset between the terminals is 1000 Hz or less, then the SNR for nearby terminals should be limited to 27 dB to ensure that the loss in SNR for other terminals is 1 dB or less. If the SNR required to achieve the highest bit rate supported by the OFDM system does not exceed 27 dB, then the SNR limit for nearby terminals of 27 dB (or 40 dB) will not have any effect on the maximum supported data rates for near terminals.

[0090] The gross power control requirements described above can be achieved by using a slow power control loop. For example, control messages can be sent as needed to adjust the power of the uplink of the near terminals (for example, when the power level changes due to movement of these terminals). Each terminal can be informed of the initial transmit power level for use on the uplink when entering the system as part of a call setup.

[0091] Groups of subbands may be assigned by the active terminal in a manner that mitigates the effect of crosstalk between subbands. In particular, high SNR terminals may be assigned subbands located close to each other upon reception. At reception, low SNRs may be assigned subbands that are close to each other, but away from the subbands assigned by the high SNR terminal at reception.

SAVE IN OFFICIAL DATA AT MULTIPLEXING OF SUB-RANGE

[0092] The ability to organize up to Q simultaneous uplink pilot transmissions reduces the overhead for the pilot by a factor of Q. The improvement may be more significant since uplink pilot transmission can represent a significant portion of the uplink phase. The amount of improvement can be numerically estimated for an illustrative OFDM system.

[0093] In such an illustrative OFDM system, the system bandwidth is W = 20 MHz and N = 256. Each sampling period has a duration of 50 nsec. A cyclic prefix of 800 nsec is used (or Cp = 16 samples), and each OFDM symbol has a duration of 13.6 μs (or N + Cp = 272 samples). An uplink pilot is transmitted in each MAC frame, which has a duration of 5 ms or 367 OFDM symbols. The pilot transmission from each terminal should have a total energy of 4 symbol periods × total transmit power. If there are K active terminals, then the total number of symbol periods used to transmit the pilot signal without multiplexing the subbands is 4 · K. For K = 12, 48 symbol periods will be used for pilot transmission on the uplink, which is approximately 13.1 of 367 symbols in the MAC frame. Service information of the pilot signal increases to 26.2% of the MAC frame in the presence of K = 24 active terminals.

[0094] If K groups of subbands are assigned to the active terminals and are allowed to transmit the pilot on the uplink at a time, then only 4 symbol periods are required in each MAC frame for the pilot transmitted on the uplink. The use of subband multiplexing for uplink pilot signal transmission reduces the overhead to 1.1% of the MAC frame for K = 12 and 2.2% for K = 24. This represents a significant savings of 12% and 24% for K = 12 and 24, respectively, for the amount of overhead required to transmit the pilot signal on the uplink.

[0095] FIG. 8A shows an uplink pilot savings graph for a different number of active terminals in the illustrative OFDM system described above. As shown in FIG. 8A, savings increase approximately linearly with the number of terminals.

[0096] The savings for an illustrative OFDM system that supports Q _R simultaneous uplink speed control transmissions can also be estimated numerically. An exemplary OFDM system has M = 224 usable subbands and uses BPSK modulation with a 1/3 coding rate. The number of information bits per modulation symbol is 1/3, and approximately 75 information bits can be sent on 224 usable subbands for each symbol period. If each terminal sends 15 bits or less of speed control information in each MAC frame, then approximately 5 terminals can be served simultaneously by one OFDM symbol. Without subband multiplexing, 5 OFDM symbols should be assigned to 5 terminals for their rate control information (each OFDM symbol will contain a large amount of equalization data for unused bits). With subband multiplexing, the same rate control information can be transmitted in a single OFDM symbol, which saves 80%.

[0097] The savings with subband multiplexing is even greater for some transmission diversity modes. For the space-time transmit diversity (STTD) scheme, each pair of modulation symbols (denoted s ₁ and s ₂ ) is transmitted over two symbol periods through two transmit antennas. The first antenna transmits the vector x ₁ = [s ₁ s ^* ₂ ] ^T for 2 symbol periods, and the second antenna transmits the vector x ₂ = [s ₂ -s ^* ₁ ] ^T for the same 2 symbol periods . The transmission unit for STTD is effectively two OFDM symbols. With subband multiplexing, information for 10 terminals can be sent in 2 OFDM symbols, which is significantly less than the 20 OFDM symbols that are required if each terminal transmits its speed control information in a separate pair of OFDM symbols.

[0098] The savings are even greater for the transmission diversity mode using 4 antennas and the transmission unit of which is 4 OFDM symbols. For this transmit diversity mode, subband multiplexing for 15 terminals in a single period of 4 symbols can be performed. The speed control information for 15 terminals can be transmitted in 4 OFDM symbols with subband multiplexing, which is significantly less than the 60 OFDM symbols that are required if each terminal transmits its speed control information in a separate set of 4 OFDM symbols.

[0099] FIG. 8B shows a graph of the savings in transmitting uplink rate control for a different number of active terminals in an illustrative OFDM system. For such a system, up to 12 terminals can be multiplexed using subband multiplexing. Each terminal can be assigned 18 subbands, with each subband carrying 3 information bits. Each of the 12 terminals has the ability to transmit 108 information bits in their assigned 18 subbands for 2 symbol periods. This is much less than 24 symbol periods that 12 terminals would need without subband multiplexing. With 12 terminals, 22 characters are saved, which is about 6% of the MAC frame with 367 OFDM symbols. If there are 24 terminals, 44 characters are saved, which is approximately 12% of the MAC frame. As shown in FIG. 8B, the savings increase approximately linearly with the number of terminals.

[0100] FIG. 8C shows a graph of savings resulting from multiplexing of subbands in pilot transmission, rate control, and uplink acknowledgment. In plot 812, pilot and rate control information for multiple terminals are implemented with subband multiplexing in pilot and speed control segments, respectively. Confirmation for this case is not considered. In graph 814, pilot, rate control information, and acknowledgment for multiple terminals are implemented with subband multiplexing in pilot, rate control, and acknowledgment segments, respectively.

[0101] As can be seen from the graphs in FIG. 8C, the savings increase approximately linearly with the number of terminals for which multiplexing is performed. In addition, savings increase as more types of information are multiplexed. It can be seen that subband multiplexing can significantly reduce the amount of overhead for pilot and signaling so that more available resources can be advantageously used for data transmission.

SYSTEM

[0102] FIG. 7 is a block diagram of an embodiment of an access point 110x and terminal 120x that are configured to support uplink subband multiplexing. At access point 110x, traffic data is provided from a data source 708 to a TX data processor 710 that formats, encodes, and interleaves the traffic data to provide encoded data. The data rate and coding can be determined by the speed control and coding control, respectively, performed by the controller 730.

[0103] OFDM modulator 720 receives and processes encoded data and pilot symbols to provide an OFDM symbol stream. The processing in the OFDM modulator 720 may include (1) modulating the encoded data to generate modulation symbols, (2) multiplexing the modulation symbols with pilot symbols, (3) converting the modulation symbols and pilot symbols to obtain the converted symbols, and (4) attaching a cyclic prefix each transformed symbol to form a corresponding OFDM symbol.

[0104] Transmitter block (TMTR) 722 receives and converts the OFDM symbol stream into one or more analog signals and performs additional processing (eg, amplifies, filters, and boosts) the analog signals to generate a downlink modulated signal suitable for transmission over a wireless channel . The modulated signal is then transmitted through an antenna 724 to the terminals.

[0105] At terminal 120x, a downlink modulated signal is received by antenna 752 and provided to receiver unit (RCVR) 754. Transmitter unit 754 performs processing (eg, filters, amplifies, and lowers the frequency) of the received signal and digitizes the processed signal to provide samples.

[0106] Then, the OFDM demodulator 756 removes the cyclic prefix attached to each OFDM symbol, converts each received transformed symbol using FFT (Fast Fourier Transform), and demodulates the received modulation symbols to provide demodulated data. The RX data processor 758 decodes the demodulated data to recover the transmitted traffic data that is provided to the data consumer 760. The processing in the OFDM demodulator 756 and the RX data processor 758 is complementary to that performed by the OFDM modulator 720 and TX data processor 710, respectively, at the access point 110x.

[0107] As shown in FIG. 7, the OFDM demodulator 756 may derive channel estimates and provide these channel estimates to a controller 770. The RX data processor 758 may provide the status of each received packet. Based on various types of information received from OFDM demodulator 756, RX data processor 758, controller 770 may determine or select a specific rate for each transmission channel. The pilot signal and uplink signaling information (e.g., rates for use for downlink data transmission, acknowledgment for received packets, etc.) may be provided by controller 770, processed by TX data processor 782, modulated in OFDM modulator 784, processed at transmitter unit 786 and transmitted via antenna 752 back to access point 110x. The pilot signal and uplink signaling information may be transmitted in a group (s) of subbands assigned to terminal 120x for these types of transmissions.

[0108] At access point 110x, an uplink modulated signal from terminal 120x is received by antenna 724, processed at receiver unit 742, demodulated in OFDM demodulator 744, and processed by RX data processor 746 to recover pilot and signaling information transmitted by the terminal. The restored signaling information is provided to the controller 730 and is used to control the processing of data transmitted on the downlink to the terminal. For example, the rate for each transmission channel may be determined based on the rate control information provided by the terminal, or may be determined based on channel estimates from the terminal. The received acknowledgment may be used to initiate retransmission of packets received with errors in the terminal. Controller 730 may also output an improved channel frequency response for each terminal based on a pilot transmitted on the assigned subbands on the uplink, as described above.

[0109] Controllers 730 and 770 control the operation of the access point and terminal, respectively. Storage devices 732 and 772 provide storage of program codes and data used by controllers 730 and 770, respectively.

[0110] The methods for transmitting pilot signaling and uplink signaling described herein can be implemented by various means. For example, these methods may be implemented in hardware, software, or a combination thereof. In the case of implementation in the form of hardware, the elements used to implement any method or their combination can be implemented in one or more specialized integrated circuits (ASIC), digital signal processors (DSP), digital signal processor devices (DSPD), programmable logic devices (PLD), in-circuit programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors and other electronic units designed to perform the functions described in the present description or combinations thereof.

[0111] In the case of implementation in the form of software, these methods can be implemented through modules (eg, procedures, functions, etc.) that perform the functions described in the present description. Software codes may be stored in a storage device (e.g., storage devices 732 or 772 in FIG. 7) and executed by a processor (e.g., controller 730 or 770). The storage device may be implemented in the processor or as external to the processor, in which case it may be connected with the possibility of exchanging data with the processor through various means known in the art.

[0112] The headings are included in the present description for reference and assistance in finding specific sections. These headings are not intended to limit the scope of the concepts described in the sections headed by them, and such concepts may be applied in other sections of the present description.

[0113] The above description of the disclosed 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 apparent to those skilled in the art, and the general principles set forth herein can be applied to other embodiments without departing from the spirit and scope of the present invention. Thus, the present invention should not be limited to the embodiments set forth in the present description, but, on the contrary, corresponds to the broadest scope consistent with the principles and features disclosed in the present description.

Claims (30)

1. A method for transmitting pilot signals on an uplink of a wireless communication system, comprising the steps of:
separating the plurality of usable subbands appropriately for use in transmitting data into at least two disjoint groups of subbands;
assigning to the terminal a first group of at least two disjoint groups;
receive pilot transmission from the terminal in the subbands of the first group. 2. The method according to claim 1, additionally containing stages in which:
assigning a second group of at least two disjoint groups to the second terminal; and receive pilot transmission from the second terminal in the subbands of the second group. 3. The method according to claim 1, additionally containing:
receiving a channel estimate for the terminal based on reception, wherein the channel estimate covers at least one subband not included in the first group. 4. The method of claim 3, wherein the channel estimate for the terminal covers a plurality of usable subbands. 5. The method according to claim 1, in which each of the at least two non-overlapping groups includes the same number of subbands. 6. The method according to claim 1, in which each group in at least two non-overlapping groups includes S subbands, wherein S is an integer greater than or equal to the number of taps for the impulse response of the uplink channel. 7. The method according to claim 1, in which the subbands in each of the at least two disjoint groups are uniformly distributed over the plurality of usable subbands. 8. The method according to claim 1, in which the transmit power used to transmit the pilot signal in each subband of the first group is set to be larger than the average transmit power per subband that would be used if the pilot signal was transmitted on all subbands, with a scale factor greater than one. 9. The method of claim 8, in which the scaling factor is equal to the number used, divided by the number of subbands in the first group. 10. The method of claim 8, in which the scaling factor for the transmit power used in transmitting the pilot signal in each subband of the first group is determined as specific per MHz, and the total transmit power is limited to the frequency band used in the wireless communication system. 11. The method according to claim 1, further comprising: controlling transmit power when transmitting a pilot signal from the terminal so that the signal-to-noise ratio (SNR) at reception for the terminal is maintained at or below a certain SNR threshold. 12. The method of claim 1, wherein the subbands in the first group assigned to the terminal are adjacent subbands in at least one other group assigned to at least one other terminal with approximately equal received pilot power. 13. The method of claim 1, wherein the wireless communication system is an orthogonal frequency division multiplexing (OFDM) communication system. 14. The method of claim 1, wherein the plurality of usable subbands are orthogonal subbands formed by OFDM. 15. An uplink pilot transmission method in an orthogonal frequency division multiplexing (OFDM) communication system, comprising the steps of:
dividing a plurality of usable subbands suitable for transmitting data into a plurality of disjoint groups of subbands, each group in a plurality of disjoint groups including the same number of subbands;
assigning one group in a plurality of disjoint groups to each of at least two terminals, wherein said at least two terminals are assigned at least two groups of subbands;
receive pilot transmission from said at least two terminals in at least two groups of subbands. 16. The method of claim 15, further comprising: deriving a channel estimate for each of the at least two terminals based on said technique, the channel estimate for each of the at least two terminals encompassing the plurality subbands used. 17. A method for transmitting a pilot signal on an uplink in a wireless communication system, comprising the steps of:
accepting an assignment of a subband group for the uplink pilot, said group including a subset of a plurality of usable subbands suitable for transmitting data;
determining transmit power for use in each of the subbands of the group, the transmit power for each subband being set higher than the average transmit power per subband, which would be used if the pilot signal was transmitted on all subbands with a scale factor greater than one; and
transmit the pilot in the subbands of the group with the specified specific transmit power. 18. A method for transmitting uplink signaling information in a wireless communication system, comprising the steps of:
dividing the plurality of usable subbands suitable for transmitting data into a plurality of disjoint groups of subbands;
assigning one group in a plurality of disjoint groups to each of at least two terminals, wherein said at least two terminals are assigned at least two groups of subbands;
receive signaling transmission within one time interval from the specified at least two terminals on at least two groups of subbands. 19. The method of claim 18, wherein the signaling transmission comprises downlink data rate control information. 20. The method of claim 18, wherein the signaling transmission contains acknowledgment for data received on the downlink. 21. The method according to p. 18, in which the transmit power used to transmit the pilot signal in each subband of the first group, set higher than the average transmit power per subband, which would be used if the transmission of the pilot signal produced on all subbands, with a scale factor greater than one. 22. The method of claim 18, wherein each group in a plurality of disjoint groups includes the same number of subbands. 23. The method of claim 18, wherein each group in a plurality of disjoint groups includes a variable number of subbands. 24. The method of claim 18, wherein it is possible to select different modulation schemes for use in each of a plurality of disjoint groups. 25. A device for receiving a pilot signal transmitted in a wireless communication system with multiple subbands, comprising:
means for dividing the plurality of usable subbands suitable for transmitting data into at least two disjoint groups of subbands;
means for assigning a first group of said at least two disjoint groups to a terminal;
means for receiving pilot transmission from the indicated terminal on the subbands of the first group. 26. The device according A.25, further comprising: means for deriving a channel estimate for the terminal based on the transmission of the pilot signal received on the subbands of the first group, wherein the channel estimate covers at least one subband not included in the first group. 27. A device for transmitting a pilot signal in a wireless communication system, comprising:
means for receiving an assignment of a group of subbands for transmitting the pilot on the uplink, said group including a subset of a plurality of usable subbands suitable for transmitting data; and
means for transmitting the pilot signal in the subbands of the specified group, and the transmit power of the pilot signal for use in each of the subbands of the group is set higher than the average transmit power per subband that would be used if the transmission of the pilot signal was performed on all subbands, with a coefficient scaling larger than one. 28. An access point in a wireless communication system, comprising:
a demodulator configured to receive pilot transmission from the terminal, wherein from the plurality of usable subbands suitable for transmitting data, a plurality of disjoint groups of subbands are formed and pilot transmission is received on a first group of subbands selected from a plurality of disjoint groups and assigned to the indicated terminal; and
a controller configured to derive a channel estimate for the terminal based on the transmission of the pilot signal, wherein the channel estimate covers at least one subband not included in said group assigned to said terminal. 29. The access point of claim 28, wherein the demodulator is further configured to receive pilot transmission from a second terminal on a second group of subbands, the second group selected from a plurality of disjoint groups and assigned to said second terminal. 30. An access point in a wireless communication system, comprising:
a demodulator configured to receive signaling transmission in the same time interval from at least two terminals, and from the plurality of usable subbands suitable for data transmission, a plurality of disjoint groups of subbands are formed and one group in a plurality of disjoint groups is assigned to each of of said at least two terminals, wherein said at least two terminals are assigned at least two groups of subbands and signaling transmission from said at least two terminals are received on said at least two groups of subbands; and
a controller configured to process signaling transmission received from said at least two terminals.

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