CN102055703A - Implementation method of radio frequency receiver of OFDM (Orthogonal Frequency Division Multiplexing) communication system - Google Patents

Abstract

The invention provides an implementation method of a radio frequency receiver of an OFDM (Orthogonal Frequency Division Multiplexing) communication system. By adopting the method provided by the invention, radio frequency or baseband signals of the OFDM communication system can be demodulated without a high-speed and high-precision analog to digital converter and a digital forward FFT (Fast Fourier Transform Algorithm) converter, and higher sampling precision can be achieved under lower power consumption, thus the method is particularly suitable for the ultra wideband OFDM communication system with numerous subcarriers.

Description

A kind of implementation method of radio-frequency transmitter of OFDM communication system

Technical field

The present invention relates generally to OFDM (OFDM, Orthogonal Frequency Division Multiplexing) implementation method of the receiver of communication system, such as ultra-wideband OFDM wireless telecommunication system, ultra-wideband OFDM line communication system etc., these systems are carried in information on a plurality of mutually orthogonal subcarriers to be transmitted, adopt method of the present invention can make the ultra-wideband OFDM communication system no longer need high-precision analog to digital converter, can also adopt the subcarrier of greater number, realize higher message transmission rate.Specifically, what the present invention relates to is to adopt a plurality of low-converters and a plurality of analog multiplier to realize the receiver of OFDM communication system, promotes the performance of ofdm system receiver.

Background technology

If ofdm system uses N subcarrier, each subcarrier can be by M selectable symbol-modulated, and the symbol table of ofdm system is made of M * N composite symbol so.

Equivalent ofdm signal through low-pass filtering can be expressed as:

$v\left(t\right)=\underset{k=0}{\overset{N-1}{\mathrm{\Σ}}}{X}_k{e}^{j2\mathrm{\πkt}/T},0\≤t\≤T$

Here { X _kBe the data symbol that is transmitted, and N is a sub-carrier number, and T is the duration of OFDM symbol, and spacing frequency 1/T makes whole subcarriers mutually orthogonal in each symbol duration, and this characteristic can be expressed as:

$\frac{1}{T}{\∫}_0^T{\left(e^{j2\mathrm{\π}{k}_{1}t/T}\right)}^{*}\left(e^{j2\mathrm{\π}{k}_{2}t/T}\right)\mathrm{dt}=\frac{1}{T}{\∫}_0^T{e}^{j2\mathrm{\π}(k_2-k_1)t/T}\mathrm{dt}={\mathrm{\δ}}_{k_1{k}_2}$

The * here represents the conjugate operation of plural number.

For fear of the intersymbol interference in multidiameter fading channel, time span is T _gProtection be placed in the front of OFDM symbol at interval, the signal that is launched in this protection at interval is a Cyclic Prefix, promptly-T _gSignal in≤t＜0 time interval and (T-T _gSignal in)≤t＜T time interval is identical, and band Cyclic Prefix in OFDM System signal indication is:

$v\left(t\right)=\underset{k=0}{\overset{N-1}{\mathrm{\Σ}}}{X}_k{e}^{j2\mathrm{\πkt}/T},-T_g\≤t\≤T$

Ofdm signal through low-pass filtering both can be that real number value also can be a complex values.The OFDM equivalent signal of the process low-pass filtering of real number value generally is used for the wire communication of transmission base band, and the DSL system is this method with regard to usefulness.The OFDM equivalent signal of the process low-pass filtering of complex values generally is used for wireless telecommunications, and the signal of emission is up-converted to a carrier frequency f _c, signal can be represented as:

Ofdm system transmits by information being loaded on a plurality of mutually orthogonal subcarriers, and system does not have the needed carrier spacing of multicarrier system, the frequency efficiency height, and systematic function is not subjected to the influence of the transmission delay (group delay) with frequency change yet.The ultra-wideband OFDM system needs at a high speed and high-precision analog to digital converter, when number of subcarriers increases, also can improve the requirement of precision of A/D converter, and the power consumption of receiver and cost are difficult to reduction.

Summary of the invention

The invention provides the especially implementation method of ultra-wideband OFDM system receiver of a kind of ofdm system, do not need at a high speed and high-precision analog to digital converter, also can use the subcarrier of greater number.Receiver is made of the following basic element of character:

1. the logical or low pass filter of one or more frequency converters and band;

2. many analog multipliers and 1 bit sigma/Δ analog to digital converter;

3. many sinusoidal wave and (or) square-wave signal source.

Employing is with the receiver of the OFDM communication system of upper-part formation, the quantity of frequency converter quantity logical with band or low pass filter is identical, the quantity of the quantity of analog multiplier and ∑/Δ analog to digital converter is the twice of number of subcarriers, and the product of the quantity of DCS digital clock source and the quantity of low-converter is more than or equal to the quantity of subcarrier.

Description of drawings

Below at first the accompanying drawing of specification of the present invention is simply introduced, and then each enforcement example of the present invention is introduced, principle and advantage of the present invention is described in conjunction with these accompanying drawings.

In the accompanying drawings:

Fig. 1 is according to the PSK of preferred embodiment design of the present invention or the structural representation of QAM receiver.

Fig. 2 is the structural representation according to part or all of subcarrier receiver in the ofdm system of preferred embodiment design of the present invention.

Fig. 3 is the structural representation according to the ofdm system receiver of a plurality of frequency converters of use of preferred embodiment design of the present invention.

Embodiment

Generally speaking, the receiver of ofdm system adopts at a high speed and high-precision analog to digital converter is sampled to baseband signal (the radio frequency ofdm system needs low-converter that radiofrequency signal is become baseband signal), with the forward fft processor data demodulates is come out then, therefore need high speed and high-precision analog to digital converter, also high to the linearity requirement of receiver.

The implementation method of ofdm system receiver provided by the invention in the requirement that has reduced the linearity, has improved the sampling precision of analog to digital converter, and the increase of expense is also in the acceptable degree.

Fig. 1 is according to the PSK of preferred embodiment design of the present invention or the structural representation of QAM (modulator approach of the subcarrier of ofdm system) receiver, the 100th, base band or Low Medium Frequency signal, the 101st, analog multiplier, 102 and 103 is sine wave or square-wave signals of same frequency, 103 phase place is than 1/4 signal period of phase delay of 102, the 104th, (sample frequency can reach GHz or higher) ∑/Δ analog to digital converter at a high speed, the 105th, the sampled clock signal of analog to digital converter, 106 and 107 is the output signals that convert digital signal to, wherein comprises the PSK that demodulates or the amplitude and the phase information of qam signal.A kind of preferable methods is to use the mutual conductance integrator to realize high speed ∑/Δ analog to digital converter.

Fig. 2 is the structural representation according to the part or all of subcarrier receiver of ofdm system of preferred embodiment design of the present invention, wherein 200 is input signals of carrier frequency, after low noise amplifier 201 amplifications, transform to Low Medium Frequency by frequency converter 202 again, logical or the low pass filter 204 of band is used for the outer or high-frequency signal of filtering band, subcarrier receiver 205 is single sub-carrier receivers shown in Figure 1, and 206 represent control signals such as 102,103 and 105, and 207 represent output signal 106 and 107.If the number of subcarrier receiver is identical with the number of ofdm system subcarrier, the frequency of each subcarrier receiver 102 and 103 signals is respectively for the frequency of ofdm system subcarrier, formed the forward FFT converter of a simulation, realized the receiver of an intact complete ofdm system, but the signal source of needs and ofdm system sub-carrier number equal number produces 102 and 103 signals.

The sub-carrier frequencies difference of supposing ofdm system is F=1/T, and sub-carrier number is N.Fig. 3 is the structural representation according to the ofdm system receiver of a plurality of frequency converters of use of preferred embodiment design of the present invention.Logical or the low pass filter of J frequency converter and band is arranged in the system shown in Figure 3, and the local oscillation signal frequency of J frequency converter differs K*F successively.If use low pass filter, its cut-off frequency need be higher than the baseband signal frequency range N*F of ofdm system, use band pass filter can obtain better receiver performance, the passband width of band pass filter is greater than K*F, preferred band pass filter centre frequency is set to N*F, and this is the expense of balancing circuitry realization and the result of rate request.Be connected to K subcarrier receiver shown in Figure 1 behind each filter respectively, the control signal 102 of K sub-carrier receiver and 103 frequency differ F successively, all total J*K the sub-carrier receiver of receiver needs only the requirement that N≤J*K just can satisfy the ofdm system receiver.

In the receiver of ofdm system shown in Figure 3, J frequency converter needs J local oscillation signal source, and J organizes every group of K demodulator needs K demodulated reference signal source, needs J+K local oscillation signal source altogether.A preferred embodiment is: for the ultra broadband ODFM system of 128 subcarriers, sample 8 frequency converters (J=8) and 16 every group demodulators (K=16) add up to and need J+K=8+16=24 local oscillation signal source.

For the ofdm system of transmission carrier frequency signaling, the frequency converter among Fig. 3 all is a low-converter.Ofdm system for transmission base band, frequency converter among Fig. 3 all is a upconverter, also can use a upconverter and a band pass filter, baseband signal is converted to carrier frequency signaling after, the ofdm system that is re-used as the transmission carrier signal is handled, and has just increased the expense of system.

Claims (7)

1. ∑/Δ D conversion method and (or) device, comprising:

   A) implementation method of exercisable mutual conductance integrator and (or) device;

   B) exercisable ∑/Δ analog-to-digital conversion control method and (or) device.
2. The implementation method of a PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation) demodulation and (or) device, comprising:

   A) implementation method of exercisable simulation PSK or QAM demodulation and (or) device;

   B) exercisable as claim 1 or similarly the analog-to-digital implementation method of ∑/Δ and (or) device.
3. The implementation method of the OFDM receiver that carrier wave arranged and (or) device, comprising:

   A) implementation method of exercisable a plurality of low-converters and (or) device;

   B) exercisable a plurality of implementation method and device as claim 2 or similar PSK or QAM demodulation.
4. The implementation method of a carrier free OFDM receiver and (or) device, comprising:

   A) implementation method of exercisable a plurality of upconverter and (or) device;

   B) exercisable a plurality of implementation method and device as claim 2 or similar PSK or QAM demodulation.
5. The implementation method of an OFDM communication system receiver and (or) device, comprising:

   A) exercisable as claim 34 or similarly receiver implementation method and (or) device;

   B) implementation method of exercisable baseband processor and (or) device.
6. 6. OFDM wireless telecommunication system or device comprise:

   A) exercisable as claim 5 or similarly receiver implementation method and (or) device;

   B) implementation method of exercisable radio frequency sending set and (or) device.
7. 7. OFDM line communication system or device comprise:

   A) exercisable as claim 5 or similarly receiver implementation method and (or) device;

   B) implementation method of exercisable transmitter and (or) device.

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