CN101375523B - Selecting MCS in a MIMO system - Google Patents

Abstract

An accurate total error rate performance can be measured using a computed error vector magnitude (EVM) per stream. Using this EVM, the receiver or the transmitter can advantageously generate an optimized modulation and coding scheme (MCS) that corresponds to a specific number of streams, modulation and coding rate for the transmitter. For example, the receiver can compute an SNR from the EVM and then use an SNR vs. MCS table to determine the optimized MCS. In contrast, the transmitter can receive an EVM-to-RSSI mapping and an EVM- to-MCS mapping from the receiver. These mappings and an EVM can facilitate selecting the optimized MCS.

Description

In mimo system, select the method for MCS

H. leaf

W-J. Cui

N. open

J.M. gilbert

Related application

The priority that No. the 60/643rd, 461, the provisional application that is entitled as " Rate Adaptation Using Closed LoopTechniques (using the rate adapted of technology of closed loop) " that the application requires to submit on January 12nd, 2005.

Background of invention

Correlation technique

The design of communication system of wireless lan (wlan) is based on the standard family of describing among the IEEE 802.11.For solving multipath, the decline and other situation of more specifically saying so and causing by multipath (wherein the various objects in the environment can reflect the wireless signal that is sent), wireless system can adopt various technology.A kind of this type of technology is that WLAN is configured to multiple-input and multiple-output (MIMO) system.

Fig. 1 illustrates the mimo system 100 of a simplification, and it can send simultaneously on a plurality of antennas and on a plurality of antennas, receive simultaneously.Specifically, transmitter (Tx) 101 can send signal simultaneously from antenna 102A (using transmitter chain 103A) with from antenna 102B (using transmitter chain 103B).Similarly, receiver (Rx) 104 can receive signal simultaneously from antenna 105A (using receiver chain 106A) with from antenna 105B (using receiver chain 106B).According to concrete realization, use a plurality of antennas ability spreading ranges, or in given scope, improve data rate.Note, also can use a plurality of antennas to send a plurality of data flow.Mimo system 100 can also advantageously minimize the poor of signal to noise ratio (snr) on the different frequency section.

In IEEE 802.11a/g standard, can use different modulation schemes to modulate the subcarrier of the channel that is associated with the OFDM code signal.Exemplary modulation scheme comprises binary phase shift keying (BPSK), QPSK (QPSK), 16 quadrature amplitude modulation (QAM), 64QAM etc.

---abbreviating coding in this article as---added the redundant possibility that accurate signal receives that also can be used to increase as signal to use convolutional encoding.Code rate is the bit number that sent and the ratio of the actual data bit number that will be sent out.For example, 1/2 code rate is meant 2 bits of per 1 actual data bits transmission.The compactest current code rate is 5/6, and wherein per 5 data bits send 6 bits.

It should be noted that and 802.11 conformances to standard that every kind of modulation scheme can have predetermined code rate.For example, table 1 is listed multiple modulation scheme that provides in 802.11a 1999 standards and the code rate that is associated thereof.

Table 1: modulation scheme and code rate

Data rate (Mb/s)	Modulation scheme	Code rate	The coded-bit of each subcarrier	The coded-bit of each OFDM code element	The data bit of each OFDM code element
						6	BPSK	1/2	1	48	24
9	BPSK	3/4	1	48	36
						12	QPSK	1/2	2	96	48
18	QPSK	3/4	2	96	72
						24	16-QAM	1/2	4	192	96
36	16-QAM	3/4	4	192	144
						48	64-QAM	2/3	6	288	192
54	64-QAM	3/4	6	288	216

In the standard mimo system, can send single or a plurality of data flow.Number, modulation and the code rate scheme (MCS) of stream can be provided with based on channel conditions.The overall performane of channel conditions is to receive signal strength indicator (RSSI).This RSSI can be used to calculate the bit error rate, and the MCS that allows directiveness thus at least selects.

Notice that white Gaussian noise possibly cause that random bit makes mistakes.These bits are made mistakes and can be used convolutional encoding easily to be corrected.Unfortunately, the bit error rate is a key element of total packet error rate performance.Specifically, the bit error rate does not comprise bursting and makes mistakes.Bursting makes mistakes possibly take place because of decline or high reject signal.These are burst to make mistakes and comprise makeing mistakes in a large number at short notice, therefore can not use convolutional encoding to correct simply.

Therefore, the standard rssi measurement is not enough to measure exactly and uses given MCS can how well successfully to send an information block.Therefore produce needs, wherein use the accurate tolerance of total error rate performance can cause optimized MCS to select the accurate tolerance of total error rate performance.

Invention field

A kind of method of in multiple-input, multiple-output (MIMO) system, selecting modulation and code rate scheme (MCS) is provided.

The accompanying drawing summary

Fig. 1 illustrates multiple-input and multiple-output (MIMO) system of a simplification.

Fig. 2 illustrates and wherein receives function is the wireless system that transmitter generates the simplification of an optimized MCS.

Fig. 3 illustrates receiver and is used for a kind of exemplary techniques that optimization MCS confirms.

Fig. 4 A illustrates receiver and is used for another exemplary techniques that optimization MCS confirms.

Fig. 4 B illustrates the exemplary SNR and the MCS relation table that can in the technology of Fig. 4 A, use.

Fig. 5 illustrates and wherein launches the wireless system of function for the simplification that self generates optimization MCS.

Fig. 6 illustrates the exemplary techniques that makes transmitter be used for confirming its oneself MCS.

Summary of the invention

The standard rssi measurement is not enough to measure exactly and uses stream, modulation and the code rate scheme (MCS) of given number can how well successfully to send an information block.According to an aspect of the present invention, calculate the accurate tolerance of total error rate performance.Can advantageously use this accurate tolerance of total error rate performance to guarantee that the MCS of height optimization selects.As following more detailed description, this MCS selects and can be carried out by receiver or transmitter.

Provide a kind of and come definite method for the transmitter optimization MCS in this wireless system by the receiver in the wireless system.In the method, receiver can receive the vague generalization map information of selected transmitting power and modulation scheme relation from the transmitter there with the form of message.For given modulation scheme, each selected transmitting power can satisfy the transmitter distortion requirement.Receiver can calculate the vector magnitude (EVM) of on average makeing mistakes according to this message (if use a plurality of streams, then being each stream).Use this EVM, receiver is with calculating signal to noise ratio (snr).

Use this SNR, receiver is with the SNR that can predict various MCS based on transmitting power and modulation scheme relation information.At this moment, receiving function uses these SNR and SNR and MCS relation table to come to confirm optimization MCS as transmitter.Notice that each MCS in SNR and the MCS relation table is in fact corresponding to a kind of data rate, wherein every kind of data rate and then have the modulation and the code rate scheme of the stream and 802.11 defineds of associated number.Notice that this SNR value is the relevant required SNR of MCS that decodes reliably.In one embodiment, can be based on emulation or lab test pre-stored SNR and MCS relation table.In one embodiment, for example can use and come dynamically to adjust SNR and MCS relation table based on the historical successful speed of SNR.

Provide another kind of and come the method for confirming for the transmitter optimization flow amount in this wireless system, modulation and code rate scheme (MCS) by the receiver in the wireless system.In the method, receiver can receive the vague generalization map information of selected transmitting power and modulation scheme relation from the transmitter there with the form of message.Under given modulation scheme, each selected transmitting power can satisfy a distortion requirement.Receiver also can receive the EVM of each stream that is calculated and sent with form of message by transmitter.

At this moment, receiver can use EVM to calculate SNR.Use this SNR, receiver is with the SNR that can predict various MCS based on transmitted power and modulation scheme relation information.At this moment, receiver can use SNR and MCS relation table to confirm optimization MCS as transmitter.In one embodiment, for example can use and come dynamically to adjust SNR and MCS relation table based on the historical successful speed of SNR.

Provide a kind of and be the definite method of himself optimization MCS in this wireless system by the transmitter in the wireless system.In the method, the emission function receives the EVM of each stream with the form of message from the receiver there.Transmitter also can the form with message receive the vague generalization map information from the receiver there.The vague generalization map information can comprise that EVM shines upon to MCS to RSSI mapping and EVM.

Use EVM and EVM to the RSSI mapping, transmitter can calculate the RSSI at receiver place.Then, use RSSI and selected transmitter power, the emission function is to the EVM at various MCS prediction receivers place.At this moment, the emission function uses EVM to shine upon for himself selecting an optimized MCS to MCS.

It should be noted that follow-up calculating can advantageously obtain SNR value and RSSI value very accurately through being that EVM begins from total error rate performance number accurately.These exact values and then can cause the selection of the height optimization of MCS.

Notice that above-mentioned technology can advantageously realize in the instruction software that realizes that uses a computer.

Detailed description of the drawings

According to an aspect of the present invention, can use the error vector magnitude (EVM) that calculates to measure total accurately error rate performance.Use this EVM, receiver or emission function are advantageously selected optimized flow amount, modulation and code rate scheme (MCS) for transmitter.

Fig. 2 illustrates the wireless system 200 of a simplification, and wherein receiver 203 can be that transmitter 201 is selected an optimized MCS 207.The message 202 that in system 200, transmitter 201 can be with comprising transmitter capabilities 204---for example available data rate---sends to receiver 203.

For clarity sake, term " ability " can be defined as the mode of operation that can carry out on the device physical.Therefore, for example, device only can have the ability that a sub-set of using the several data speed that 802.11 standards that are suitable for are allowed is sent/received.To use through the basic speed (for example 802.11a is 6Mbps, and 802.11g is 1Mbps) of consulting---be exemplary capability---with this data rate sends another device to.

Notice that message 202 can comprise one or more command packet (for example, RTS (request is sent) divides into groups) and/or one or more subsequent data packet.In any situation, message 202 all will comprise the preamble that contains training signal and data-rate information.Message 202 can with minimum and therefore the most sane speed be sent out, for receiver 203 advantage of calculating MCS 208 is provided thus.

After receiving, receiver 203 can calculate the information that obtains from message 202, i.e. the error vector magnitude of each stream (EVM).Receiver 203 can use this information that obtains 206, transmitter capabilities 204, its oneself receiver ability 205 and out of Memory 207 to be transmitter 201 to confirm the suitable MCS that use in this case.

In one embodiment, out of Memory 207 can be including, but not limited to the interference in the environment.For example, channel possibly have relatively low gain for required information, and for example the send-receive path possibly have zero gain (that is, carrier wave 5 is very weak usually when receiving signal) at carrier wave 5.To cause carrier wave 5 to have significant amount of energy suddenly with carrier wave 5 consistent interference.Therefore, do not describe channel itself, disturb the environment that to describe carrier wave 5 although disturb.Therefore, any interference all can influence the selection of optimization MCS significantly.

Receiver 203 can feed back to transmitter 201 with the result with various means.For example; Send additional message so that the overhead of MCS information to be provided in order to reduce; Still guarantee simultaneously frequent updating, can MCS 208 be embedded in the control frame (for example, confirming that (ACK) divides into groups) or compound frame (for example data+CF-ACK divides into groups) that SIFS sent after the time.

Fig. 3 illustrates receiver and is used for optimizing a kind of exemplary techniques 300 that MCS confirms.Notice that transmitter can reduce its power and carry out more complicated modulation to reduce distortion.That is, the non-linearity of the power amplifier in the transmitter chain can make the transmission distorted signals.This distortion increases with the power that is used for sending signal with being directly proportional.Higher modulation has the stricter requirement of restriction to transmitter distortion.Transmitter can be initially satisfies the transmitting power that this distortion requires for given modulation scheme selection one is known.This Initial Trans is called as " compensation " power sometimes.

In step 301, use this Initial Trans, the emission function is sent to receiver with the vague generalization map information of selected transmitting power and modulation scheme relation.It should be noted that each selected transmitting power also can satisfy the distortion requirement under given modulation scheme.

In step 302, receiver can be according to this message (if use a plurality of streams, then being each stream) error of calculation vector magnitude (EVM).Notice that EVM can advantageously assess the quality of signals through digital modulation through confirming that the actual reception signal is many near the optimized constellation positions consistent with suitable modulation scheme.In other words, can EVM be defined as the poor of the expection complex value of demodulated symbol and symbol value that actual reception arrives.Therefore, EVM can comprise amplitude and phase error information.

In step 303, receiver can use EVM to calculate signal to noise ratio (snr).Specifically, SNR be signal power than last noise power, i.e. signal power/(error amplitude) ²Use this SNR, receiver is with coming to be each MCS prediction SNR based on general transmitting power and modulation scheme relation information in step 304.

At this moment, receiver can be confirmed optimized MCS based on SNR and MCS relation table in step 305.

In one embodiment, can dynamically adjust SNR and MCS relation table based on out of Memory.For example, SNR information possibly can't reflect successful speed fully.Therefore; In one embodiment, this table also can comprise a historical successful speed, thereby if actual successful speed is superior to the successful speed that is associated with the SNR that calculates; Then this table will recommend to use a higher speed (that is, complicated modulation and encoding scheme).On the contrary, if actual successful speed is inferior to the successful speed that is associated with the SNR that calculates, then this table will recommend to use a lower speed (being lower modulation of complexity and encoding scheme).

In one embodiment, can use channel symmetry in transmitter, to concentrate more complicated calculating.In this technology shown in Fig. 4 A, calculate the EVM (it should be suitable with the EVM of each stream that calculates at receiver) of each stream based on its communication that receives at last from receiver at step 401 transmitter.In step 402, transmitter is sent to receiver with this EVM that is calculated by transmitter (Tx EVM) and general transmitter power and modulation scheme relationship map information.In step 403, receiver can calculate corresponding SNR according to Tx EVM.Notice that this SNR calculates required computational resource and significantly is lower than the required computational resource of EVM calculating.In step 404 and use the SNR calculate, receiver is with can being that each MCS predicts SNR based on transmitting power and modulation scheme relation information.In step 405, receiver can use SNR and MCS relation table to confirm optimization MCS.At this moment, receiver can send to transmitter with this MCS.It is particularly favourable that technology 400 especially has the occasion that realizes in the device of the confined space or computational resource at receiver at for example laptop computer etc.

Fig. 4 B illustrates the exemplary SNR and the MCS relation table 410 that can in step 405, use.In one embodiment, table 410 can use emulation or lab measurement to generate.Notice that the MCS in the table 410 is meant single current and the 2nd MCS is meant double fluid (for example, MCS0 be meant single current and MCS8 is meant double fluid).In one embodiment, the minimum value during the SNR of double fluid is two SNR---being SNR of each stream---.

It should be noted that the related SNR (and therefore be considered to each MCS sensitivity) that each MCS is existed this MCS that can be used to decode reliably.Receiver for the step 404 (Fig. 4 A) of each MCS prediction SNR afterwards; Can search SNR and MCS relation table at step 405 receiver; For example whether SNR and MCS relation table 410 (Fig. 4 B) are higher than required SNR and pick up the flank speed that the foot that is full requires subsequently with the SNR that checks prediction.Notice that table 410 also can be indicated fluxion.

Fig. 5 illustrates that wherein transmitter 501 can be for himself selecting the simplification wireless system 500 of optimization MCS.In system 500, transmitter 501 can send to receiver 503 with message 502.Receiver 503 can obtain information 504 from message 502, for example the RSSI of each stream and EVM.Receiver 503 sends to transmitter 501 through message 505 with EVM information and map information 508 (being discussed below) subsequently.In addition, receiver 503 can also be with the form transmitter-receiver ability 504 of message 505, for example spendable data rate.Notice that message 502 and 505 can comprise one or more orders and/or packet.After receiving message 505; Transmitter 501 (for example can use EVM/ mapping 508, receiver ability 507, the generator ability 506 of himself and resulting information 509; EVM) and out of Memory 510 (for example, the interference in the environment) come the MCS that under this environment, share for itself confirming.

Fig. 6 illustrates the exemplary techniques 600 that transmitter is used for confirming its oneself MCS.The message (for example, message 505) that in step 601, receiver can send to transmitter and comprise the vague generalization map information---being EVM to MCS map information and EVM to the RSSI map information---.In one embodiment, this vague generalization map information can be sent out in correlation time, and can randomly be updated at follow-up time based on the historical information that receiver is followed the tracks of.

In step 602, divide into groups for each that receives from transmitter, receiver is beamed back the EVM of each stream.In step 603, transmitter uses this information and EVM to shine upon the RSSI that calculates the receiver place to RSSI.In step 604, this RSSI allows transmitter to be directed against the EVM at each MCS prediction receiver place with the transmitting power of himself with the EVM that calculates.Then, in step 605, transmitter can use receiver EVM to shine upon to MCS and select to use optimized MCS.

Although combined accompanying drawing that exemplary embodiment of the present invention has been carried out detailed explanation, yet should be appreciated that the present invention is not limited to those accurate embodiment at this.They be not exhaustive or the present invention is defined in disclosed precise forms.Therefore many modifications and variation will be obvious.For example, notice that the technology described in Fig. 3 and 4 can be applicable to multicast message with being equal to, transmitter can send to some receivers with information termly in this situation.Notice that in addition above-mentioned steps can use the computer implemented instruction that is included in receiver or the transmitter to be achieved.

In one embodiment, average EVM (asking average on all sections) can be used to the MCS selection.In another embodiment, the EVM of each each section of stream can be used to the MCS selection.Note, can reflect interfere information (for example, forming the part of out of Memory 207/510 (Fig. 2 and Fig. 5)) among the EVM.

In one embodiment, transmitter can use a robust M CS to send a frame as detection, and use feedback information to confirm the MCS that share rapidly subsequently at the beginning and behind the certain hour of stopping using.That is, under the situation of the above-mentioned message that can send various types of information of unfavorable usefulness, transmitter can be appealed to survey and caused some feedback.If transmitter fails to receive feedback, then it can select more sane MCS for follow-up transmission.Yet, be by with due to the conflicting of another frame if transmitter is confirmed losing of feedback, transmitter can select not reduce MCS.Similarly, transmitter can be once in a while send the data flow more data stream that has sent than it and the EVM information that obtains each more complete stream selected to be used for MCS with sane modulation and encoding scheme.

In one embodiment, as confirming substituting of fluxion based on SNR and MCS relation table, fluxion can be based on the EVM of each stream.For example, if the EVM of two streams is close and very little, then can use the double fluid of phase same rate.Relative with it, if is the EVM of a stream than another little [what? ], then can use the double fluid of different rates.If the EVM of second stream is very big, then can use single current.

Notice that above-mentioned all technology can advantageously provide in the instruction software that realizes that uses a computer.In one embodiment, these instructions can reside on the computer-readable medium.

Therefore, scope of the present invention is intended to limited accompanying claims and come thereof.

Claims (6)

1. one kind is come the method for confirming for the transmitter optimization fluxion in the said radio MIMO system, modulation and code rate scheme (MCS) by the receiver in wireless multiple-input and multiple-output (MIMO) system, and said method comprises:

Form receiver/transmitter power and the modulation scheme relationship map information from said transmitter there with message, for given modulation scheme, each transmitting power can make distortion minimization;

According to said message error of calculation vector magnitude (EVM);

Use said EVM to calculate signal to noise ratio (snr);

For each MCS prediction SNR, make up a SNR and MCS relation table based on said SNR and said transmitter power and modulation scheme relationship map information thus; And

Use said SNR and MCS relation table to come to confirm optimized MCS for said transmitter.

2. the method for claim 1 is characterized in that, said SNR and MCS relation table are that dynamic adjustable is whole.

3. method as claimed in claim 2 is characterized in that, said SNR and MCS relation table comprise the historical successful speed based on SNR.

4. one kind is the method for confirming of transmitter optimization fluxion, modulation and code rate scheme (MCS) in the said radio MIMO system by the receiver in wireless multiple-input and multiple-output (MIMO) system, and said method comprises:

Form receiver/transmitter power and the modulation scheme relationship map information from said transmitter there with message, for given modulation scheme, each selected transmitting power can make distortion minimization;

The error vector magnitude (EVM) that reception is calculated by said transmitter and sends with form of message;

Use said EVM to calculate signal to noise ratio (snr);

Coming based on said SNR and said transmitter power and modulation scheme relationship map information is each MCS prediction SNR, makes up a SNR and MCS relation table thus; And

Use said SNR and MCS relation table to come to confirm optimized MCS for said transmitter.

5. method as claimed in claim 4 is characterized in that, said SNR and MCS relation table are that dynamic adjustable is whole.

6. method as claimed in claim 5 is characterized in that, said SNR and MCS relation table comprise the historical successful speed based on SNR.

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