Reverse link power control in an orthogonal system

(Claim of priority under 35 USC 119) This patent application is assigned to the assignee and expressly incorporated herein by reference, "FH-OFDMA Reverse-Link Power" filed on July 20, 2004. Claim the priority of US Patent Provisional Application No. 60 / 589,823 entitled "Control)".

(Field) The present invention generally relates to communication and, more specifically, to techniques for determining reverse link power control in an orthogonal communication system.

(background) In a Frequency-Hopping Orthogonal Frequency Division Multiple Access (FH-OFDMA) system, the bandwidth is evenly divided into multiple orthogonal subcarriers. Each user is given multiple of these OFDM subcarriers. In FH-OFDMA, users will also hopping over the entire bandwidth (ie, the subset of OFDM carriers assigned to each user will change over time). All users in the same sector or cell are orthogonal to each other and therefore do not cause interference with each other.

FH-OFDMA is an efficient multiplexing technology for high data rate transmission over wireless channels. However, due to the wide range of signal-to-noise ratio (SNR) fluctuations in FH-OFDMA systems, checking small packet error rates on all transmissions is extremely resource inefficient. Packet retransmission mechanisms (eg, H-ARQ) are often used to help avoid such inefficiencies.

In addition, a closed-loop power control is often used to ensure that sufficient SNR (ie, the SNR required to close the communication link) is received at the base station. .. There is a unique trade-off between the number of transmissions allowed (retransmission) and the transmission power required for successful transmission. Increasing the transmission power level, for example, may reduce the number of transmissions required for successful transmission, which directly contributes to higher data rates. Alternatively, if the number of allowed transmissions (retransmissions) increases, the transmission power required for successful transmission may decrease. This trade-off between unique rate and power adaptation makes designing a power control loop for systems with retransmissions a significant task.

Therefore, there is a technical need for a technique that trades off rate and power in an effective way that takes retransmission into account.

[wrap up] On the one hand, the reverse link power control method is to send the packet, determine if the packet was received without error, and if the packet is error-free. Decrease the effective carrier-to-interference (C / I) setpoint if received, and if the packet was not received without error. , To increase the effective C / I setpoint.

On the one hand, the method of reverse link power control further comprises determining if Received Power Over Thermal (RpOT) is greater than Maximum Received Power Over Thermal (RpOTmax). On the one hand, the method of reverse link power control further comprises issuing a down command if RpOT is not greater than RpOTmax.

On the one hand, the method of reverse link power control has an effective carrier-to-interference ratio (C / I) rather than an effective carrier-to-interference ratio for the setpoint (C / Isp). Further prepare to judge whether it is small or not. On the one hand, the method of reverse link power control further comprises determining if the received power overthermal (RpOT) is less than the minimum received power overthermal (RpOTmin).

On the one hand, the method of reverse link power control is such that if the effective carrier-to-interference ratio (C / I) is not less than the effective carrier-to-interference ratio (C / Isp) for the setpoint, or received power over. It is further provided to issue a down command if the thermal (RpOT) is not less than the minimum received power overthermal (RpOTmin).

On the one hand, the reverse link power control method is such that if the effective carrier-to-interference ratio (C / I) is smaller than the effective carrier-to-interference ratio (C / Isp) for the setpoint, and the received power overthermal If (RpOT) is less than the minimum received power overthermal (RpOTmin), it is further provided to issue an up command.

On the one hand, it determines if the packet was received without error, reduces the effective carrier-to-interference (C / I) setpoint if the packet is received without error, and if the packet is error-free. The step of increasing the effective C / I setpoint if not received without it comprises outer loop power control.

On the one hand, the reverse link power control method is if Received Power Overthermal (RpOT) is less than or equal to Minimum Received Power Overthermal (RpOTmin), or if Received Power Overthermal (RpOT) is Maximum. Received power overthermal RpOTmax or higher is further provided with disabling the outer loop power control.

On the one hand, the reverse link power control method is such that if the received power overthermal (RpOT) is larger than the minimum received power overthermal (RpOTmin) and the received power overthermal (RpOT) is the maximum received power. If it is less than the overthermal RpOTmax, it further comprises enabling outer loop power control.

On the one hand, the wireless communication device provides a means for transmitting the packet, a means for determining whether the packet was received without error, and an effective carrier-to-interference if the packet was received without error. It comprises means for reducing the (C / I) setpoint and, if the packet was not received without error, means for increasing the effective C / I setpoint.

On the one hand, the processor is programmed to perform a method of estimating interference in a wireless communication system, which method is to send a packet and determine if the packet was received without error. And, if the packet is received without error, reduce the effective carrier-to-interference (C / I) setpoint, and if the packet is not received without error, the effective C / I setpoint. To increase and be equipped.

On the one hand, a computer-readable medium embodies a method of reverse link power control, which is to send a packet, determine if the packet was received without error, and if the packet is received. Decreasing the effective carrier-to-interference (C / I) setpoint if received without error, and increasing the effective C / I setpoint if the packet was not received without error. , Equipped with.

Various aspects and embodiments of the present invention will be described in more detail below.

[Detailed description] The features and essence of the present invention will become more apparent from the detailed description described below, along with the drawings in which similar reference characters identify similarly throughout.

The term "exemplary" as used herein means "an example, an instance, or an illustration." Any embodiment or design described herein as "exemplary" should not necessarily be construed as preferred or advantageous over other embodiments or designs.

The techniques described here for performance based rank prediction include various communication systems, such as code division multiple access (CDMA) systems, wideband CDMA (WCDMA) systems, and direct sequence CDMA (). DS-CDMA) system, Time Division Multiple Access (TDMA) System, Frequency Division Multiple Access (FDMA) System, Fast Downlink Packet Access (HSDPA) System, Orthogonal Frequency Division Multiple Access (OFDM) Based System, Orthogonal Frequency Division Multiple Access (FDMA) System It can be used for connection (OFDMA) systems, single-input single-output (SISO) systems, multi-input multi-output (MIMO) systems, and so on.

OFDM is a multi-carrier modulation technique that effectively divides the entire system bandwidth into multiple (NF) orthogonal subbands. These subbands are also called tones, subcarriers, bins, and frequency channels. In OFDM, each subband is associated with each subcarrier that can be modulated with data. Modulated symbols up to NF can be transmitted over the NF subband during each OFDM symbol period. Prior to transmission, these modulated symbols are NF-point inverse fast Fourier to obtain a "transformed" symbol containing an NF chip. It is transformed into a time-domain using transform (EFFT).

The OFDMA system can utilize OFDM to support multiple users at the same time. For frequency hopping OFDM systems, each user's data is transmitted using a specific frequency hopping (FH) sequence assigned to the user. The FH sequence indicates the specific subband used for data transmission during each hop period. Multiple data transmissions for multiple users can be sent simultaneously using different FH sequences. These FH sequences are defined to be orthogonal to each other so that only one data transmission uses each subband during each hop period. By using an orthogonal FH sequence, intra-cell interference is avoided, and multiple data transmissions do not interfere with each other while enjoying the benefits of frequency diversity.

Typically, the power control loop can be split into two parts: an inner loop and an outer loop. The base station is such that the desired quantity set by the power control outer loop (eg, signal-to-interference-and-noise ratio (SINR), etc.) is maintained by the user. Issue UP / DOWN power control commands as directed by the inner loop to adjust the transmit power of. The outer loop dynamically adjusts this setpoint so that the identified quality of service (QoS) is met regardless of the changing channel state.

IS-95 and CDMA2000 use packet error rate (PER) as the quality of service metric of choice. In essence, the power control loop adjusts the transmit power so that the PER is close to the target setpoint (eg 1%). However, there are some drawbacks to such algorithms when applied to systems with retransmissions.

For example, consider a best-effort application if a packet error is declared only when the packet is not received correctly after the maximum number of allowed transmissions has been reached. The packet error rate-based (PER-based) power control algorithm attempts to minimize transmit power while attempting to maintain the target packet error rate. As the maximum number of transmissions allowed increases, the transmission power required decreases (assuming the packet size remains the same). User transmit power has decreased, but throughput has also decreased.

Interestingly, in a CDMA system, the processing power of each individual user is reduced, but because more users are added to the system (in a CDMA system, less interference is more supportable users). (Remember that it leads), sector processing power can remain unchanged (or even increase). Unfortunately, systems that use orthogonal multiple access techniques on reverse links (eg, TDMA, FDMA, and OFDMA) will suffer overall sector throughput loss with this power control scheme. Let's go.

In an orthonormal system, when all of the dimensions are used and entered, no additional users can be added without breaking the orthogonality between the users. Therefore, adding more users does not necessarily help compensate for the sector processing power loss caused by the reduction in processing power of each individual user in the orthogonal system.

FIG. 1 shows a wireless multiple access communication system 100 according to one embodiment. System 100 includes a plurality of base stations 110 that support communication for a plurality of wireless terminals 120. A base station is a fixed station used for communication with terminals and may be referred to as an access point, or node B, or in some other term.<u style="single">Cell 102 is typically illustrated as a hexagon for exemplary purposes and, as is well known in the art, for terminals associated with cell sites or base stations. Define the coverage area (defines). The cell can be divided into multiple sectors 104.</u>The terminals 120 are typically distributed throughout the system, and each terminal may be fixed or mobile. Terminals may also be referred to as mobile stations, user equipment (UE), or wireless communication devices, or in some other term. Each terminal can communicate with one or more base stations on forward and reverse links at any time. This depends on whether the device is active, soft handoff is supported, and whether the device is in soft handoff. For simplicity, Figure 1 only shows the transmission over the reverse link. The system controller 130 couples to base stations 110 to provide coordination and control for these base stations, and further controls the routing of data for terminals serviced by these base stations. To do.

A closed-loop power control scheme for an FH-OFDMA system with a hybrid ARQ (H-ARQ) will be described below according to this embodiment. It will be apparent to those skilled in the art that the algorithms described below can be easily modified to work in any orthogonal system (eg, TDMA, FDMA) that uses retransmission.

This algorithm uses best-effort traffic (eg, ftp, downloads, etc.) and latency-sensitive constant bit rate (CBR) traffic (eg, voice, multimedia). , Etc.) are both designed to work well. For best effort traffic, the proposed algorithm alleviates the problem of rate loss due to the coupling between power control and H-ARQ. For latency-sensitive CBR traffic, the proposed power control algorithm attempts to minimize the user's transmit power while still meeting the packet error rate and latency constraints. The same underlying power control algorithms and interfaces can be used for both best effort and latency sensitive CBR traffic.

FIG. 2 shows a flowchart 200 of outer loop power control according to an embodiment. The goal of the outer loop is to set the target effective carrier-to-interference (C / I) for the inner loop to track. The effective C / I is used, for example, instead of the average C / I. Effective C / I is a better measure of channel condition than average C / I in an FH-OFDMA system. The "effective SNR" is (proportional) to the geometric mean averaged over all tones.

The outer loop is updated when (i) there is a packet error or (ii) the packet is correctly decrypted. Due to retransmission, the outer loop may not be updated every time a packet arrives.

A packet is considered to be in error if it is not successfully decrypted after the specified maximum number of transmissions arrives, or if its latency exceeds the specified latency limit. Is done. Latency includes both queuing delay and transmission delay.

By declaring a packet with a latency higher than the maximum latency allowed as a packet error, the latency constraint is seamlessly incorporated into the power control loop. The rationale behind this is that in most real-time applications, as far as the user's perception is concerned, corrupted or delayed packets are more or less equally harmful, so delayed packets are simply discarded. It means that it will be done. In addition, to help further regulate packet latency, packets can be dropped at the transmitter (even if they send packets whose latency has already exceeded the limit, they will receive them. It doesn't make sense because it is discarded by the machine anyway).

The receiver can detect that some packets have been canceled by the transmitter by detecting that the packets are received out of sequences. These missing packets are treated as packet errors. Lost packets can only be detected once the next packet in the sequence has been correctly decrypted by the receiver. In essence, corrupted packets, canceled packets and packets with excessive latency are declared as packet errors, and the outer loop sets the effective C / I to keep the packet error rate at the target value. Adjust points dynamically. By selecting the step size when properly adjusting the effective C / I setpoint, the target PER can be controlled to the desired value.

At step 202, a check is made to determine if the setpoint is to be updated. If not, then the control flow returns to step 202 of the next iteration. If the setpoint is to be updated, then the control flow proceeds to step 204.

In step 204, a check is made to determine if there is a packet error. If there are no packet errors, then the control flow proceeds to step 206. Otherwise, the control flow proceeds to step 208.

At step 206, a check is made to determine if the packet is missing. If the packet is lost, then the control flow proceeds to step 208 and the effective C / I setpoint is increased. Otherwise, the control flow proceeds to step 210 and the effective C / I setpoint is reduced.

As shown in Figure 3, the base station then uses the inner loop to issue up / down power control commands (eg +/- 1dB). FIG. 3 shows a flowchart 300 of inner loop power control according to one embodiment.

The outer loop can be disabled when no data exists. Therefore, in the absence of data, only inner loop control is enabled.

The inner loop is updated periodically (eg, every few hops / slot). The base station measures the received signal power and effective C / I over the measurement interval. The inner loop attempts to maintain the target effective C / I set by the outer loop, while still satisfying the RpOT constraint (ie, the behavioral RpOT should be between RpOTmin and RpOTmax). Received power overthermal (RpOT) is defined as the ratio between received signal power (P) and thermal noise (No). The inner loop of this proposed algorithm attempts to meet both the effective C / I and RpOT targets.

Setpoints (eC / Isp, RpOTmin, RpOTmix) are user-specific. Users with different quality of service (QoS) can have different RpOTmin, max constraints. Updates are also user-specific.

RpOTmin and RpOTmax can be determined according to QoS. RpOTmin and RpOTmax can be set equal to each other.

Although not shown in the figure, the outer loop update is disabled according to one embodiment when the RpOT limit (ie RpOTmin or RpOTmax) is reached. This is to prevent the effective C / I setpoint from being incremented or decremented indefinitely.

There are two advantages to incorporating RpOT into a power control design. First, since RpOT does not depend on interference power from other users, by regulating transmit power based on RpOT, the power control loop is inherently stable (ie, indefinite between users). There is no power race). Second, by constraining the operating range of RpOT, transmit power can be traded off for data rate.

Without further constraints on the RpOT operating range, the power control loop can drive transmit power to very low levels, because it is all that is required to meet the specified packet error rate requirements. Because it can be. As mentioned earlier, this leads to lower processing power. By enhancing the operating range of the RpOT, the user can effectively choose the trade-off between the data rate and the transmission power (for example, the user can transmit early by transmitting at a higher power). You can enjoy higher rates from termination)). In fact, RpOTmin helps protect against unwanted rate loss, while RpOTmax helps ensure stable operation.

By setting RpOTmin = RpOTmax, the outer loop is effectively disabled. In practice, the base station regulates the user's transmit power to meet the target RpOT. This setting may be used to support best effort traffic, where users can always benefit from having higher data rates.

In step 302, a check is made to determine if the inner loop is to be updated. If not, then the control flow returns to step 302 of the next iteration. If the inner loop is to be updated, then the control flow proceeds to step 304.

In step 304, a check is performed to determine if RpOT&gt; RpOTmax. If yes, then the control flow proceeds to step 306 and a down command is issued by the base station. If not, then the control flow proceeds to step 308.

In step 308, a check is made to determine if the effective C / I is less than the effective C / Isp or if RpOT &lt;RpOTmin. If yes, then the control flow proceeds to step 310, and the base station issues an up command. If no, then the control flow proceeds to step 306 and the base station issues a down command.

In one embodiment, a hysteresis function is added to the update functions of the outer and inner loops 200, 300 of FIGS. 2 and 3, respectively. Hysteresis functions help prevent the system from entering a limit cycle.

In one embodiment, the packet error automatically becomes an up command to speed up recovery (assuming, of course, that the RpOT constraint is not violated).

In one embodiment, the inner loop continues to be executed when only the control channel is present, but the outer loop is disabled. When the data channel comes back, the behavior of the outer loop can be seamlessly resumed. Therefore, the same underlying power control loop is used for both control and data channels.

FIG. 4 shows a block diagram of an embodiment of the base station 110x and the terminal 12Ox. On the reverse link, at terminal 12Ox, the transmit (TX) data processor 510 processes the reverse link (RL) traffic data (eg, formats, encodes, interleaves, and modulates), and Provides a modulation symbol for traffic data. The TX data processor 510 also processes control data from controller 520 (eg, CQI) and provides modulation symbols for the control data. Modulator (MOD) 512 processes traffic and control data modulation and pilot symbols, and a sequence of complex-valued chips. chips) is provided. Processing by the TX data processor 510 and modulator 512 is system dependent. For example, if the system utilizes OFDM, the modulator 512 can perform OFDM modulation. The transmitter unit (TMTR) 514 conditions the sequence of chips (eg, converts to analog, amplifies, filters, and frequency upconverts) and produces a reverse link signal. , The reverse link signal is sent through the transmitter / receiver (D) 516 and via the antenna 518.

At base station 110x, the reverse link signal from terminal 12Ox is received by antenna 552, sent through transmit / receive switch 554, and fed to receiver unit (RCVR) 556. The receiver unit 556 conditions the received signal (eg, filters, amplifies, and frequency downconverts (frequency). downconvert)), and further digitize the conditioned signal to obtain a stream of data samples. The demodulator (DEMOD) 558 processes the data sample to obtain symbol estimates. The receive (RX) data processor 560 then processes the symbol estimates to obtain the decoded data for the terminal 12Ox (eg, deinterleave and decode). The RX data processor 560 also performs erase detection and supplies the controller 570 with the status of each received codeword used for power control. The processing performed by the demodulator 558 and the RX data processor 560 is complementary to the processing performed by the modulator 512 and the TX data processor 510, respectively.

The process for forward link transmission can be performed in the same manner as for the reverse link described above. The process for the transmission of reverse and forward links is typically specified by the system.

For reverse link power control, the SNR estimator 574 estimates the received SNR for the terminal 12Ox and supplies the received SNR to the TPC generator 576. The TPC generator 576 also receives the target SNR and generates a TPC command for the terminal 12Ox. The TPC command is processed by the TX data processor 582, further processed by the modulator 584, conditioned by the transmitter unit 586, sent through the transmit / receive switch 554, and sent to the terminal 12Ox via the antenna 552.

At terminal 12Ox, the forward link signal from base station 110x is received by antenna 518, transmitted through transmit / receive switch 516, conditioned and digitized by receiver unit 540, processed by demodulator 542, and further. Processed by the RX data processor 544 to get the received TPC command. The TPC processor 524 then detects the received TPC command to obtain the TPC decision used to generate the transmit power adjustment control. The modulator 512 receives control from the TPC processor 524 and adjusts the transmit power for reverse link transmission. Forward link power control can be achieved in a similar manner.

Controllers 520 and 570 direct the operation of various processing knits inside the terminal 12Ox and the base station 110x, respectively. Controllers 520 and 570 can also perform various functions for power control and erasure detection for forward and reverse links. For example, each controller can implement an SNR estimator, TPC generator, and target SNR adjustment unit for that link. The controller 570 and RX data processor 560 can also implement the processes 200 and 300 in Figures 2 and 3. Memory units 522 and 572 store data and program code for controllers 520 and 570, respectively.

The elimination detection and power control techniques described herein can be implemented by a variety of means. For example, these technologies can be implemented in hardware, software or a combination thereof. For hardware implementations, the processing units used to perform erasure detection and / or power control are one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices ( DSPD), Programmable Logical Devices (PLDs), Field Programmable Gate Arrays (FPGAs), Processors, Controllers, Microcontrollers, Microprocessors, Other Electronic Units Designed to Perform the Functions Described Here, or Combinations thereof. Can be implemented in.

In the case of software implementation, the techniques described herein can be implemented in modules that perform the functions described herein (eg, processing procedures, functions, etc.). The software code can be stored in a memory unit (eg, memory unit 572 in FIG. 5) and executed by a processor (eg, controller 570). The memory unit can be implemented inside or outside the processor, in which case it can be communicatively coupled to the processor via various means as known technically. it can.

The above description of the disclosed embodiments is provided to allow any person skilled in the art to make or use the present invention. Various modifications of these embodiments will be readily apparent to those of skill in the art, and the general principles defined herein apply to other embodiments without departing from the spirit and scope of the invention. Can be done. Therefore, the present invention is not intended to be limited to the embodiments presented herein, and should be given the broadest scope consistent with the principles and novel features disclosed herein.

<figref num="1">FIG. 1 shows a wireless multiple access communication system 100 according to one embodiment.</figref><figref num="2">FIG. 2 shows a flowchart of outer loop power control according to one embodiment.</figref><figref num="3">FIG. 3 shows a flowchart of inner loop power control according to one embodiment.</figref><figref num="4">FIG. 4 shows a block diagram of a terminal and a base station.</figref>