CN101232485B - Communication system with carrier deviation estimating feedback - Google Patents

Abstract

The invention discloses a communication system, comprising: a carrier offset estimation module for determining carrier frequency offset of an input signal; a rotator for rotating the input signal to minimize the carrier frequency offset and produce compensation signal; a correlator for associating the compensation signal to a unique word so as to obtain correction of timing; an equalizer for equalizing the compensation signal based on the correction of timing and producing an equalized signal; and a carrier frequency correction module for guiding a second carrier offset according to the result of the correlator and undergoing re-rotation based on the second carrier offset.

Description

Communication system, PHS receiver and be used for the method for operation communication system

The cross reference of related application

The U.S. Patent application No.11/442 that the application relates on May 30th, 2006 and submits to, 838, incorporate by reference the full content of this application here into.

Technical field

Relate generally to wireless communication system of the present invention more specifically relates to a kind of carrier deviation estimating feedback device and with the communication system of this device.

Background technology

Wireless communication system such as cellular system allows the user wirelessly transmitting and receive data between the user and/or between user and cell base station.Generally speaking, wireless communication system must operate under a certain characteristic frequency, and power level is lower than a certain particular power level.Under these constraints, wireless system is attempted maximization for each user's data transmission, and simultaneous adaptation is shared the every other user's of wireless system demand.Therefore, each wireless device must come maximum data to transmit with the distribution bandwidth intelligently.

Developed several method for maximizing the use that distributes bandwidth, wherein a kind of is time division multiple access (TDMA).The communication system that the dissimilar employing TDMA of many kinds is arranged.The communication system of a kind of TDMA of use is personal handyphone system (PHS), and PHS is the mobile telephone system in a kind of 1.88-1.93GHz of being operated in frequency band.Because the low-cost advantage of PHS, PHS is widely used at present.Generally speaking, PHS has the through-put power of 500mW and the scope of 10-100 rice.

PHS uses TDMA to modulate (ADPCM) as audio coder ﹠ decoder (codec) (codec) as radio interface and adaptive difference pulse code.Audio coder ﹠ decoder (codec) is included in analog to digital converter (ADC) and the digital to analog converter (DAC) of changing between the analog-and digital-form.TDMA is the digital data transmission scheme that a plurality of users of a kind of permission access single radio frequency (RF) channel.The interference of interchannel is by being avoided for the unique time slot of each user assignment in each channel.For example a PHS frame comprises four channels: a control channel and three traffic channel.

With reference now to Fig. 1,, the PHS telephone system comprises the PHS phone 10 with antenna 12 and the cell base station 11 with antenna 13.Exemplary PHS phone 10 comprises signal processing module 16, memory 22, power supply 24 and I/O module 26.Signal processing module 16 comprises sending module 18 and receiver module 20.I/O module 26 can comprise various user interfaces, for example microphone 26-1, loud speaker 26-2, display 26-3, keyboard 26-4 and camera 26-5 etc.

Sending module 18 will be converted to the PHS compatible signal from user's input of microphone 26-1.The data that receiver module 20 will be received from antenna 12 are converted to the user and can identify form, and export via loud speaker 26-2.Signal processing module 16 usefulness memories 22 are processed the data that send to antenna 12 and receive from antenna 12.Power supply 24 is to phone 10 power supplies.

Generally by 0 and 1 representative, these 0 and 1 are called as the position to numerical data.Data are normally utilized the baseband signal of beared information that amplitude, frequency or the phase place of carrier signal are modulated and are sent.Quadrature Phase Shift Keying (QPSK) is a kind of phase-modulation that is commonly used in the communication system.In QPSK, information bit is grouped into and is called the right of dibit (dibit).Thereby QPSK represents dibit value 00,01,10 and 11 with four symbols.QPSk is with these four sign map to four constant phase angles.For example, symbol 00 can be mapped to+3 π/4.On the other hand, PI/4-DQPSK is used differential coding, and wherein the mapping between symbol and the phase angle changes.In addition, PI/4-DQPSK is mapped to real and empty phase angle with in these four symbols each, thereby causes 8 constellation types to distribute.

Fig. 2 is the schematic diagram of exemplary PHS time slot format.The implication of each field in control channel (CCH) and the traffic channel (TCH) will be described below.Fig. 3 shows for the current demodulation mechanism of CCH data.

As known to the skilled person, the demodulation performance of wireless communication system depends on many factors, for example noise, intersymbol interference, frequency shift (FS), timing offset etc.If other factors are better, then the precision of carrier shift estimation is not very important just, if but other factors are relatively poor, and then the precision of carrier shift estimation will have important impact to whole performance, and this is by being verified.

In addition, notice that the demodulation mechanism of Fig. 3 is only applicable to control channel, i.e. CCH, above problem is non-existent for TCH, loop is revised carrier shift because we have adopted AFC.

We find in practice, and the demodulation mechanism of Fig. 3 can not realize the carrier shift estimation well.That is, when lower or intersymbol interference was more serious as SNR, the performance that we find CCH by emulation was more than the poor performance of TCH, and obviously, this is because the inexactness that current carrier shift is estimated causes.

Summary of the invention

In one aspect, the invention discloses a kind of communication system, comprising: the carrier shift estimation module of determining the carrier frequency shift of input signal; Rotate described input signal to minimize described carrier frequency shift and generation through the circulator of compensating signal; With described relevant with unique word to obtain the correlator of correction of timing through compensating signal; Balanced described through compensating signal and generate equalizer through equalizing signal based on described correction of timing; And the result who utilizes described correlator derives the carrier frequency correcting module of the second carrier shift amount again to be rotated according to described the second carrier shift amount.

In another aspect, the invention discloses the method for a kind of operation communication system, comprising: the carrier frequency shift of determining input signal; Rotate described input signal to minimize described carrier frequency shift and to generate through compensating signal; With described relevant with unique word to obtain correction of timing through compensating signal; Also generate through equalizing signal through compensating signal based on described correction of timing equilibrium is described; And utilize described correlated results to derive the second carrier shift amount, and again be rotated according to described the second carrier shift amount.

Description of drawings

Fig. 1 is exemplary PHS telephone system;

Fig. 2 is the schematic diagram of exemplary PHS time slot format;

Fig. 3 shows the demodulation mechanism of current C CH data;

Fig. 4 is the block diagram of the part of receiver data path;

Fig. 5 is the functional block diagram of carrier recovery block 118;

Fig. 6 is the demodulation mechanism according to CCH data of the present invention;

Fig. 7 is the signal flow graph in the carrier shift correcting module 136 of Fig. 6; And

Fig. 8 is the window schematic diagram of smooth window summer 322.

Embodiment

Describe exemplary embodiment of the present invention in detail below with reference to accompanying drawing.

With reference now to Fig. 4,, Fig. 4 shows the block diagram for the part in the receive data path of the individual station (PS).Notice that in RX path, i/q signal has become baseband signal after through RF and IF down-conversion.Hereinafter, unless otherwise indicated, otherwise all refer to the base band situation.AFE (analog front end) (AFE) part 110 comprises the analog to digital converter 112 that input signal is converted to digital input signals from analog input signal.Digital signal after the conversion is transferred to hardware accelerator module 114.Hardware accelerator module 114 is processed digital input signals, and generation has compensated the signal behind the carrier frequency shift.

Hardware accelerator module 114 comprises decimation filter 116, and decimation filter 116 is with N times of character rate (for example, three times of character rates, 576kHz) input signal of formation through accelerating.N is the integer greater than 0.Input signal through accelerating is transferred to carrier recovery block 118 and circulator 120 from decimation filter 116.The output of circulator 120 is transferred to memory register 122, and for the present embodiment, memory register 122 comprises two or A/B buffer register 122.Carrier recovery block 118 detects burst, and the frequency shift (FS) between the signal of estimating to receive and send, and this will be discussed in more detail below.

Then, circulator 120 compensating carrier frequencies are to form through rotating signal.Then, be stored in and be transferred to digital signal processor (DSP) 124 through rotating signal in the A/B buffer register 122, DSP 124 comprises equalizer 126, is application self-adapting judgement equalizer 126 in the situation of unique word (UW) in the burst at training sequence.In addition, obtain relevant timing via correlator 128.It is relevant with UW to input data, therefore, after detecting the peak of correlated results, has just determined that the UW position is with respect to the timing in the bursty data.

In the coherent demodulation of psk signal, the carrier frequency shift that causes owing to the Doppler effect of limited oscillator precision or moving vehicle can cause the obvious decline of performance.In the PHS system, cell base station may have the skew up to ± 2ppm, and the individual station may have the skew up to ± 10ppm.Correcting frequency shift helps to improve receiver performance and alleviates requirement to oscillator precision in demodulation, thus Cost reduction.

Fig. 5 shows the structured flowchart of carrier recovery block 118.Carrier recovery block 118 comprises burst detector 130 and carrier offset calculator 132.Burst detection triggers signal from burst detector 130 arrives carrier offset calculator 132 from delay buffer 134, to derive carrier frequency shift.Resulting skew is transformed to the anglec of rotation, and is delivered to circulator shown in Figure 1 120, thereby can compensate the frequency shift (FS) that receives in the signal.The carrier offset calculator 132 employed algorithms that recover for carrier wave will be discussed in more detail below.

The algorithm that is used for the carrier wave recovery that is used among the PHS is open loop carrier shift algorithm for estimating.This algorithm has utilized the characteristic of PR signal (seeing Fig. 2) in the PHS system, and direct estimation is moved the carrier shift of introducing by oscillator and Doppler.The below describes this algorithm in detail.

After modulation, transmitted signal is expressed as follows:

$s\left(t\right)=\underset{k}{\mathrm{\Σ}}{g}_r(t-\mathrm{kT})\cos ({\mathrm{\ω}}_{c}t+\mathrm{\θ}\left(t\right))$

G wherein _r(t) be the root-raised cosine shaping filter, ω _cCarrier frequency, the T is-symbol cycle.θ (t) is phase modulation.In PHS, θ (t)=θ (t-T)+Δ θ (t), and send symbol (a _k, b _k) and Δ θ (k) between contact as shown in table 1 below:

Table 1 symbol is to the mapping of phase place

(a k，b k)	Δθ(k)
		(0，0)	π/4
(0，1)	3π/4
		(1，1)	-3π/4
(1，0)	-π/4

In receiver one side, use the root-raised cosine matched filter, then, the baseband signal that demodulates can be expressed as follows:

s _r(t)＝A(t)cos(Δω _ct+θ′(t)+φ)+n(t)

Wherein And g (t) is raised cosine pulse, Δ ω _cBe carrier shift, θ ' is the receiver phase modulation (t), and φ is the fixed phase offsets between the transmitter and receiver, and n (t) is white Gauss noise.

Suppose

Wherein S _rGripping altogether (t).Then

X(t)＝σ _Ae ^{j[2Δωt+θ(t)-θ(t-2T)]}+N(t)

σ wherein _A=E{A (t) ², and N (t)=E{S _r(t) n ^*(t-2T) }+E{n (t) S _r ^*(t-2T) }+E{n (t) n ^*(t-2T) } be noise item, can ignore for simplicity.

In PHS, leading (PR) pattern (seeing Fig. 2) is " 1001 ".Can derive following formula from the periodic nature of PR:

θ(t)-θ(t-2T)＝-π/2

X _I(t)＝E{A ²(t)}Sin(2ΔωT)

X _Q(t)＝E{A ²(t)}cos(2ΔωT)

X wherein _I(t) and X _Q(t) be respectively homophase and the quadrature component of X (t).

If for the cumulative X of N symbol _I(t) and X _Q(t) (wherein N is search window), then

${\mathrm{Acq}}_i\left(k\right)=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{x}_I(t_0+{\mathrm{kT}}_s+\mathrm{nT})$

And ${\mathrm{Acq}}_q\left(k\right)=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{x}_Q(t_0+{\mathrm{kT}}_s+\mathrm{nT}).$

Envelope is defined as

Amp(k)＝Acq _i ²(k)+Acq _q ²(k)

K=0 wherein, 1 ... m-1 and 0≤t ₀≤ T.T _sSampling period (T=mT _s), the number of sampled point in the m is-symbol cycle.After detecting burst, can be by finding the max{Amp (k) in the length of window N, k=0,1 ... m-1 estimates carrier shift Δ f _cSuppose Amp (k0)=max{Amp (k) | k=0,1 ... m-1}, wherein A ₀=A ²(t ₀+ k ₀T _s+ nT), and n=0 ... .N-1, then carrier shift can be estimated as $\mathrm{\Δ}{f}_c=\mathrm{\Δ}{\mathrm{\ω}}_c/2\mathrm{\π}=\frac{1}{4\mathrm{\πT}}{\tan }^{-1}\left(\frac{{\mathrm{Acq}}_i\left(k_0\right)}{{\mathrm{Acq}}_q\left(k_0\right)}\right).$

Below with reference to the demodulation mechanism of Fig. 6 description according to CCH data of the present invention.In mechanism shown in Figure 6, added a carrier shift correcting module 136.This module can be used to autocorrelative result and improve the precision that carrier shift is estimated.

Fig. 7 is the signal flow graph in the carrier shift correcting module 136 of Fig. 6.As shown in Figure 7, come the optimal sample of autocorrelator 128 to enter smooth window summer 322,322 pairs of sample summations of smooth window summer N time, N is the integer greater than 0.The output of smooth window summer 322 is by differentiator 324 differential.According to the result of differential, carrier offset calculator 326 is calculated the second carrier shift amount (for the carrier shift that the carrier offset calculator 132 in the carrier recovery block 118 calculates).The the second carrier shift amount that calculates is inputted in the circulator 120 again as rotation angle θ, and circulator 120 is rotated again according to the carrier shift amount that this calculates, thereby eliminates carrier shift.Notice that than the carrier shift that carrier offset calculator 132 calculates, the second carrier shift amount is less.And carrier offset calculator 326 can utilize the mode identical with carrier offset calculator 132 to realize.Implementation about carrier offset calculator 132 sees also the U.S. Patent application No.11/442 that quotes, and 838, be not described in detail here.

The smooth window length of smooth window summer 322 can be selected as both having comprised the PR field, comprises again the UW field, and its length of window is configurable, as shown in Figure 8.

Although more than described according to some embodiment of the present invention, it will be understood by those skilled in the art that the present invention is not limited to these embodiment.Concrete scope of the present invention should be defined by the following claims.

Claims (7)

1. communication system comprises:

Determine the carrier shift estimation module of the carrier frequency shift of input signal;

Rotate described input signal to minimize described carrier frequency shift and generation through the circulator of compensating signal;

With described relevant with unique word to obtain the correlator of correction of timing through compensating signal;

Balanced described through compensating signal and generate equalizer through equalizing signal based on described correction of timing; And

Utilize the result of described correlator to derive the carrier frequency correcting module of the second carrier shift amount again to be rotated according to described the second carrier shift amount,

Wherein said carrier frequency correcting module comprises:

Reception is from the output of described correlator and the smooth window summer of suing for peace by smooth window;

The output of described smooth window summer is carried out the differentiator of differential; And

Calculate the carrier offset calculator that described the second carrier shift amount also outputs to described the second carrier shift amount described circulator according to the differential result.

2. communication system as claimed in claim 1, the length of window of wherein said smooth window summer is configurable.

3. communication system as claimed in claim 1, the carrier frequency shift that wherein said the second carrier shift amount is determined less than described carrier shift estimation module.

4. PHS receiver that comprises communication system as claimed in claim 1.

5. the method for an operation communication system comprises:

Determine the carrier frequency shift of input signal;

Rotate described input signal to minimize described carrier frequency shift and to generate through compensating signal;

With described relevant with unique word to obtain correction of timing through compensating signal;

Also generate through equalizing signal through compensating signal based on described correction of timing equilibrium is described; And

Utilize described correlated results to derive the second carrier shift amount, and again be rotated according to described the second carrier shift amount,

The step of wherein utilizing described correlated results to derive the second carrier shift amount comprises:

Receive described correlated results and sue for peace by smooth window;

Result to described smooth window summation carries out differential; And

Calculate described the second carrier shift amount according to the differential result.

6. method as claimed in claim 5, the length of wherein said smooth window is configurable.

7. method as claimed in claim 5, wherein said the second carrier shift amount is less than determined carrier frequency shift.

Images