CN101753166B - CCK modulation method in wireless local area network - Google Patents

Abstract

The invention discloses a CCK modulation method in a wireless local area network, which inputs by 5 bits and outputs by 16 chips. The method comprises the following steps: the first two bits of the input 5 bits are used for DQPSK modulation to obtain relative phase; the last 3 bits of the last 5 bits are mapped into three QPSK phases. The implementation method of the complementary code keying codeword structure in the wireless local area network adopts a novel multi-phase complementary code construction method, so the ratio of the bit rate to the chip rate is between 2/n and 1/2 with more grades, the adaptation with different rates of a communication environment is convenient, and the performance of technical implementation is improved.

Description

CCK modulator approach in a kind of WLAN (wireless local area network)

Technical field

The invention belongs to the processing method in a kind of wireless LAN communication field, specifically, belong to the spread spectrum modulation technique in a kind of Resistant DS Spread Spectrum System.

Background technology

In the prior art, Resistant DS Spread Spectrum System is widely used, and can be applicable in the WLAN (wireless local area network), for example IEEE 802.11b standard.In IEEE 802.11b standard, use the spread spectrum mode that is called complementary code keying (CCK, Complementary Code Keying), in fact can regard the mode that spread spectrum, coding and modulation combine as.

The code word of CCK (or claim frequency expansion sequence) is the mutual-complementing code of leggy, and existing quasiorthogonal property has again preferably autocorrelation performance aperiodic.Owing to quasiorthogonal property is arranged, so the Euclidean distance between code word is larger, in additive white Gaussian noise (AGWN, Additive White Gaussian Noise) channel better performance is arranged.Because preferably autocorrelation performance is arranged, therefore in frequency selective fading channels, can produce rake, receiver adopts RAKE (rake shape) to receive can obtain preferably performance.

Different from the spread spectrum mode of general Resistant DS Spread Spectrum System, CCK is in conjunction with coding and spread spectrum, so the availability of frequency spectrum is than the height of general Resistant DS Spread Spectrum System.Owing to these reasons, adopt CCK as the spread spectrum mode of two-forty version among the IEEE802.11b.

In IEEE 802.11b, CCK becomes 4 phase places with the input bit sequential coding, and 4 phase places are combined into 8 phase places, and the chip sequence of corresponding 8 QPSK (four phase translation keyings) modulation reaches the purpose of spread spectrum.

When input bit was 4, the ratio of bit rate and spreading rate was 1/2 (being referred to as CCK1/2), altogether can produce 16 possible frequency expansion sequences this moment.When input bit was 8, the ratio of bit rate and spreading rate was 1/1 (being referred to as CCK 1/1), altogether can produce 256 possible frequency expansion sequences this moment.

The Euclidean distance of the code word of CCK 1/2 is greater than the Euclidean distance of CCK 1/1, so better performances, but spectrum efficiency is lower, is suitable for the lower communication environment of signal to noise ratio.

In IEEE 802.11b, more the spread spectrum mode of low speed does not adopt the mode of CCK, but the direct point of modulation symbol is multiplied by frequency expansion sequence, is similar to like this (n, a 1) coded system.The ratio of the bit rate of this mode and spreading rate is 1/n or 2/n (wherein n is frequency expansion sequence length, is 11 in IEEE802.11b), and its spectrum efficiency is extremely low, but autocorrelation performance is better than CCK 1/2 and CCK 1/1, so better performances.

So in existing CCK, the ratio of bit rate and spreading rate is from 2/n to 1/2, intermediate gap is larger, does not bring into play to greatest extent systematic function, and prior art has yet to be improved and developed.

Summary of the invention

The purpose of this invention is to provide CCK modulator approach in a kind of WLAN (wireless local area network), solve all lower problems of the spectrum efficiency that exists in the prior art and coding gain.

The CCK modulator approach is to input the output of 16 chips with five bits in the WLAN (wireless local area network) provided by the invention, specifically may further comprise the steps:

Steps A is used for the DQPSK modulation with the first two bit of five bits of input, obtains relative phase;

Step B is with rear three phase places that bit mapping is three QPSK of five bits of input.

In described steps A, the phase place of last chip sequence is added that relative phase is as the phase place of current chip sequence.

In described step B, rear three phase places that bit mapping is following three QPSK:

The corresponding phase place of each bit, fixing

Then be combined into 16 phase places according to following formula:

Corresponding 16 QPSK output of above-mentioned 16 phase places chip.

CCK modulator approach provided by the present invention, by constructing new codeword structure, so that the ratio of its bit rate and spreading rate is between 2/n and 1/2, its spectrum efficiency is higher than the situation of 2/n, autocorrelation and coding gain are better than the situation of CCK 1/2, and its spreading gain is than both high (frequency expansion sequence length is 16).

Description of drawings

Fig. 1 is the module diagram of the related spread spectrum modulator of CCK modulator approach of the present invention;

Fig. 2 is the performance comparison schematic diagram of the inventive method and existing CCK method.

Embodiment

Below in conjunction with accompanying drawing, will be described in more detail the present invention.

CCK can be regarded as a subclass of Golay mutual-complementing code---leggy Golay mutual-complementing code, and the building method of leggy Golay mutual-complementing code is as follows:

Order Represent pair of sequences (0≤φ ₀≤ 2 π, 0≤φ ₁≤ 2 π, 0≤φ ₂≤ 2 π), A then ₂With B ₂The adequate condition that becomes complementary series is φ ' ₂=φ ₃+ φ ₁-φ ₀+ π.

Simply be designated as phasing matrix

$\left[\begin{array}{c}{A}_2\\ {\mathrm{<figure-callout\; id="2"\; label="B"\; filenames="H2008102179523E00021.png"\; state="\{\{state\}\}">B</figure-callout>}}_2\end{array}\right]=\left[\begin{array}{cc}{\mathrm{\&phi;}}_0& {\mathrm{\&phi;}}_1\\ {\mathrm{\&phi;}}_2& {\mathrm{\&phi;}}_2^{\&prime;}\end{array}\right]$

Any length is the complementary series A of N _NAnd B _NCan be generalized to the complementary series that length is 2N by cascade, also be

A _2N＝(A _NB _N)， $B_{2N}=\left(A_N{\stackrel{\&OverBar;}{B}}_N\right)$

Wherein Upper line represent phase rotating π.

So can obtain with the mode of cascade length and be 4 complementary series. $\left[\begin{array}{c}{A}_4\\ B_4\end{array}\right]=\left[\begin{array}{cccc}{\mathrm{\&phi;}}_0& {\mathrm{\&phi;}}_1& {\mathrm{\&phi;}}_2& {\mathrm{\&phi;}}_2^{\&prime;}\\ {\mathrm{\&phi;}}_3& {\mathrm{\&phi;}}_1+\mathrm{\&Delta;}& {\mathrm{\&phi;}}_2+\mathrm{\&Delta;}+\mathrm{\&pi;}& {\mathrm{\&phi;}}_2^{\&prime;}+\mathrm{\&Delta;}+\mathrm{\&pi;}\end{array}\right]---(2-21)$

Δ=φ wherein ₃-φ ₀Here B ₄No longer equal

But added a phase difference, obtain the degree of freedom of a phase place, namely

The phase place that adds does not affect complementary characteristic.

In fact, CCK 1/1 and CCK 1/2 can be by the suitable φ that chooses ₀, φ ₁, φ ₂, φ ₃Value, and satisfying φ ' ₂=φ ₂+ φ ₁-φ ₀+ π and Δ=φ ₃-φ ₀Under the condition, obtain by top form.Specifically, suppose

Be four phase places that obtain by modulation, order

Obtain Be updated to A ₄And B ₄In and cascade obtain A ₈=(A ₄B ₄), the chip sequence of Here it is CCK.

For the ratio of constructing bit rate and spreading rate less than 1/2 CCK code word, CCK modulator approach of the present invention increases a phase place

Obtain the sequence of 16 chips, as shown in Figure 1.Similarly write out a length and be 8 complementary series:

$\left[\begin{array}{c}{A}_8\\ B_8\end{array}\right]$

$=\left[\begin{array}{cccccccc}{\mathrm{\&phi;}}_0& {\mathrm{\&phi;}}_1& {\mathrm{\&phi;}}_2& {\mathrm{\&phi;}}_2^{\&prime;}& {\mathrm{\&phi;}}_3& {\mathrm{\&phi;}}_1+{\mathrm{\&Delta;}}_3& {\mathrm{\&phi;}}_2+{\mathrm{\&Delta;}}_3+\mathrm{\&pi;}& {\mathrm{\&phi;}}_2^{\&prime;}+{\mathrm{\&Delta;}}_3+\mathrm{\&pi;}\\ {\mathrm{\&phi;}}_4& {\mathrm{\&phi;}}_1+{\mathrm{\&Delta;}}_4& {\mathrm{\&phi;}}_2+{\mathrm{\&Delta;}}_4& {\mathrm{\&phi;}}_2^{\&prime;}+{\mathrm{\&Delta;}}_4& {\mathrm{\&phi;}}_3+{\mathrm{\&Delta;}}_4+\mathrm{\&pi;}& {\mathrm{\&phi;}}_1+{\mathrm{\&Delta;}}_3+{\mathrm{\&Delta;}}_4+\mathrm{\&pi;}& {\mathrm{\&phi;}}_2+{\mathrm{\&Delta;}}_3+{\mathrm{\&Delta;}}_4& {\mathrm{\&phi;}}_2^{\&prime;}+{\mathrm{\&Delta;}}_3+{\mathrm{\&Delta;}}_4\end{array}\right]$

And order

The chip sequence that finally obtains is:

In this CCK sequence, spectrum efficiency is 5/8, can be referred to as CCK 5/8; Detect through emulation experiment, the incoherent detection performance under awgn channel is near CCK 1/2.

In order to obtain better performance, can obtain the better code word of correlation by the code word number that reduces CCK.Get

For 5 bits of input, two bits use the DQPSK modulation like this

3 bits are chosen in 8 code words, and the cross correlation of these 8 code words is better than 256 original code words.Can be referred to as CCK5/16, detect by experiment and can see that its performance is better than CCK 1/1 and CCK1/2 under awgn channel, even be better than MOK 6/64 (M ary quadrature keying, employing length is 64 Walsh code, and BPSK is adopted in modulation), but spectrum efficiency is high more a lot of than MOK 6/64.

The complexity of the CCK 5/16 that constructs by the inventive method is lower than CCK 1/1, near CCK1/2.Listed correlator number in the detector of CCK and MOK (M-ary Orthogonal Keying, M-ary orthogonal keying) in the following table.

Table: correlator number in the detector of CCK and MOK

?	The relevant detection	Incoherent detection
			CCK?1/1	256	64
CCK?1/2	16	4
			CCK?5/16	32	8
MOK?6/64	64	64

The spectrum efficiency of CCK 5/16 is about 1/2 times of CCK 1/2, so CCK 1/1, CCK 1/2 and CCK 5/16 can be used as three kinds of spread spectrum modulation technique of multirate system.In order to improve performance, also can construct the lower CCK of spectrum efficiency, for example CCK 6/32 etc. with reference to the inventive method.

Can obtain a series of CCK code word with reference to the inventive method, their spectrum efficiency is (log ₂M+1)/and M, wherein M is code word size.As shown in Figure 2, Fig. 2 has disclosed the performance of the CCK 5/16 under awgn channel, and (abscissa is the bit energy signal to noise ratio, ordinate is bit error rate), compare with two kinds of codeword structures of prior art, the performance that can see CCK 5/16 is best (code check is lower), even (M ary quadrature keying, employing length are 64 Walsh code to be better than MOK 6/64, BPSK is adopted in modulation), but spectrum efficiency is high more a lot of than MOK 6/64.

It is to realize that the present invention can be combined in the IEEE 802.11b system, as the additional spread spectrum mode of CCK 1/1 and CCK1/2.The suitable signal to noise ratio that is higher than CCK 2/n when the communication environment signal to noise ratio, and when being lower than the suitable signal to noise ratio of CCK 1/2, system can adopt this spread spectrum mode, the bit rate that acquisition is higher than CCK 2/n, than CCK 1/2 reliable transmission performance, thereby provide codeword structure and the communication performance mode of the environmental requirement of more adaptation different communications.

Should be understood that, above-mentioned comparatively concrete for description of the invention, can not therefore think the restriction to scope of patent protection of the present invention, scope of patent protection of the present invention should be as the criterion with claims.

Claims (2)

1. CCK modulator approach in the WLAN (wireless local area network) is characterized in that inputting the output of 16 chips with five bits, specifically may further comprise the steps:

Steps A is used for the DQPSK modulation with the first two bit of five bits of input, obtains relative phase;

Step B is with rear three phase places that bit mapping is three QPSK of five bits of input;

In described step B, rear three phase places that bit mapping is following three QPSK:

The corresponding phase place of each bit, fixing And be combined into 16 phase places according to following formula:

Corresponding 16 QPSK output of above-mentioned 16 phase places chip.

2. CCK modulator approach in the WLAN (wireless local area network) according to claim 1 is characterized in that: in described steps A, the phase place of last chip sequence is added that relative phase is as the phase place of current chip sequence.

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