HK1138693B

HK1138693B - Method and system for an ofdm joint timing and frequency tracking system

Info

Publication number: HK1138693B
Application number: HK10104013.3A
Authority: HK
Inventors: 马克‧肯特
Original assignee: 美国博通公司
Priority date: 2008-08-01
Filing date: 2010-04-23
Publication date: 2014-05-30

Description

Method and system for processing communication signals

Technical Field

The present invention relates to signal processing in communication systems, and more particularly, to a method and system for OFDM joint time-frequency tracking.

Background

Mobile communications have changed the way people communicate, and mobile phones have shifted from luxury items to essential parts of everyday life. The use of mobile phones is determined by the current state of society and is not hindered by geography or technology. Voice connections can meet basic communication needs, while mobile voice connections will penetrate deeper into everyday life. Mobile networks have become a popular source of everyday information and, of course, use simple, generic mobile access technologies to access such information.

Third generation cellular networks are specifically designed to meet future mobile network requirements. With the popularity and use of these services, factors such as cost-effective optimization of network capacity and quality of service (QoS) will become more important to cellular operators than today. These factors can be achieved through careful network planning and operation, improvement of transmission means, and improvement of reception technology level. Finally, carriers need these techniques: allowing increased throughput as well as providing higher quality of service performance and speed than those offered by cable modems and/or DSL service providers. Today, advances in multiplexed antenna technology and other physical layer technologies have begun to dramatically increase the available communication data rates.

Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present application as set forth in the remainder of the present application with reference to the drawings.

Disclosure of Invention

A method and/or system for OFDM joint time and frequency tracking, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims.

According to an aspect of the invention, a method of processing a communication signal is proposed, the method comprising:

tracking a carrier frequency and a symbol time of an Orthogonal Frequency Division Multiplexing (OFDM) signal based on at least one reference symbol set; and

adjusting a frequency and a time of a receiver based on the tracked carrier frequency and symbol time.

Preferably, the method further comprises tracking the carrier frequency by generating an output signal as a function of the frequency offset Δ f (frequency offset).

Preferably, the method further comprises generating a guard time Δ t by generating a guard time Δ t_g(guard time) to track the symbol time (symbol timing).

Preferably, the method further comprises performing a fast fourier transform on the received OFDM signal to generate the set of Reference Symbols (RS).

Preferably, the method further comprises fine tuning the frequency and time of the receiver.

Preferably, prior to the fine adjustment, the method further comprises coarsely adjusting the receiver frequency and the time.

Preferably, the method further comprises generating a coarse adjustment of the receiver frequency and the time based on processing of the primary and secondary synchronization signals.

Preferably, the reference symbol set includes a number of time-frequency slots (time-frequency slots).

Preferably, the plurality of time-frequency gaps vary in accordance with a time-frequency drift (time-frequency) and a pseudo-noise sequence used to modulate the set of reference symbols.

Preferably, the OFDM signal conforms to the Long Term Evolution (LTE) signal standard of the Universal Mobile Telecommunications Standard (UMTS).

Preferably, the method further comprises controlling the adjustment of the receiver frequency by a receiver frequency oscillator (TXCO).

Preferably, the method further comprises controlling the adjustment of the time by a time generator.

According to another aspect of the present invention, there is provided a system for processing a communication signal, comprising:

one or more circuits to at least:

tracking a carrier frequency and a symbol time of an Orthogonal Frequency Division Multiplexing (OFDM) signal based on a reference symbol set; and

adjusting a frequency and a time of a receiver based at least on the tracked carrier frequency and symbol time.

Preferably, the one or more circuits track the carrier frequency by generating an output signal as a function of the frequency offset Δ f.

Preferably, the one or more circuits track the symbol time by generating an output signal as a function of the guard time Δ tg.

Preferably, the one or more circuits perform a fast fourier transform on the received OFDM signal to produce the set of reference symbols.

Preferably, the one or more circuits fine-tune the receiver frequency and the time.

Preferably, said one or more circuits also coarsely adjust said receiver frequency and said time prior to said fine adjustment.

Preferably, the one or more circuits generate the coarse adjustment of the receiver frequency and the time based on processing of a primary synchronization signal and a secondary synchronization signal.

Preferably, the set of reference symbols comprises a number of time-frequency slots.

Preferably, the plurality of time-frequency gaps vary in dependence on a time-frequency drift and a pseudo-noise sequence used to modulate the set of reference symbols.

Preferably, the one or more circuits control the adjustment of the receiver frequency by a receiver frequency oscillator (TXCO).

Preferably, the one or more circuits control the adjustment of the time by a time generator.

These and other advantages, aspects, novel features, and details of particular embodiments of the invention are more fully understood from the following description and drawings.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

fig. 1A is a diagram illustrating exemplary cellular multipath communications between a base station and a mobile processing terminal in accordance with an embodiment of the present invention.

Fig. 1B is a diagram of an exemplary MIMO communication system in accordance with an embodiment of the present invention.

Fig. 2 is a diagram of an exemplary OFDM symbol stream in accordance with an embodiment of the present invention.

Fig. 3 is a schematic diagram of an exemplary OFDM frequency and time acquisition and tracking system in accordance with an embodiment of the present invention.

Fig. 4 is a flow chart of frequency and time acquisition and tracking according to an embodiment of the invention.

Detailed Description

The invention provides a method and a system for tracking OFDM (orthogonal frequency division multiplexing) combined time frequency. The method and system of OFDM joint time-frequency tracking includes tracking a carrier frequency and a symbol time of an Orthogonal Frequency Division Multiplexing (OFDM) signal based on at least one reference symbol set. The frequency and time of the receiver are adjusted based on the tracked carrier frequency and symbol time.

The carrier frequency is tracked by generating an output signal as a function of the frequency offset af. The symbol time is tracked by generating an output signal as a function of the guard time Δ tg. A received OFDM signal is fast fourier transformed to generate a set of Reference Symbols (RSs). Coarse adjustments are made before fine adjustments to the receiver frequency and time. The receiver frequency and time are coarsely adjusted based on the processing of the primary and secondary synchronization signals. The reference symbol set includes a plurality of time-frequency gaps that vary depending on a time-frequency drift and a Pseudo Noise (PN) sequence used to modulate the reference symbols. The PN generation sequence is determined by the base station identifier. And the base station identifier may be determined by a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS). The OFDM signal conforms to the Long Term Evolution (LTE) signal standard of the Universal Mobile Telecommunications Standard (UMTS). The adjustment of the receiver frequency is controlled by a receiver frequency oscillator (TXCO) and the adjustment of the time is controlled by a time generator.

Fig. 1A is a diagram illustrating exemplary cellular multipath communications between a base station and a mobile processing terminal in accordance with an embodiment of the present invention. Referring to fig. 1A, it can be seen that a building 140, such as a home or office, a mobile terminal 142, a factory 124, a base station 126, a car 128, and communication paths 130, 132, 134 are included.

The base station 126 and the mobile terminal 142 may comprise suitable logic, circuitry, and/or code that may enable the generation and processing of MIMO communication signals.

The base station 126 and the mobile terminal 142 communicate wirelessly through a wireless channel. The wireless channel includes multiple communication paths, such as: communication paths 130, 132, and 134. The wireless channel dynamically changes as the mobile terminal 142 and/or the automobile 128 move. In some cases, the mobile terminal 142 is located within a line of sight (LOS) of the base station 126, and in some cases, there is no direct LOS between the mobile terminal 142 and the base station 126, and radio signals are transmitted by reflection in communication paths between the communicating entities, such as the exemplary communication paths 130, 132, 134. The radio signal is reflected by man-made structures such as the building 140, the factory 124, or the automobile 128, or by natural obstacles such as mountains. The system is referred to herein as a non-line-of-sight (NLOS) communication system.

Signals in a communication system include a line-of-sight (LOS) signal portion and a non-line-of-sight (NLOS) portion. If a line of sight (LOS) signal portion is present, the LOS signal portion is much stronger than a non-NLOS signal portion. In some communication systems, non line of sight (NLOS) portions can create interference and degrade receiver performance. This is known as multipath interference. For example, the communication paths 130, 132, 134 may reach the mobile terminal 142 with different delays. The communication paths 130, 132, 134 may also experience varying degrees of attenuation. For example, in the downlink, the signal received at the mobile terminal 142 is the sum of the communication paths 130, 132, and/or 134 with different attenuations, and the communication paths 130, 132, 134 are asynchronous and dynamically changing. Such a channel is called a multipath fading channel (multipath channel). Multipath fading channels introduce interference and also provide diversity and freedom for the radio channel. A communication system having a plurality of antennas at a base station and/or a mobile terminal, for example, a MIMO (Multiple-Input Multiple-output) system, is particularly suitable for obtaining a large performance gain from a multipath fading channel by using the characteristics of a radio channel. Multipath fading channels can significantly increase the performance of a communication system, particularly an NLOS (non line of sight) communication system, having a single antenna at both the base station 126 and the mobile terminal 142. Also, Orthogonal Frequency Division Multiplexing (OFDM) systems are suitable for multiplexing wireless systems.

Fig. 1B shows a schematic diagram of a MIMO communication system according to an embodiment of the invention. Referring to fig. 1B, a MIMO transmitter 102 and a MIMO receiver 104 are included, as well as antennas 106, 108, 110, 112, 114, 116. MIMO transmitter 102 includes a processor module 118, a memory module 120, and a signal processing module 122. The MIMO receiver 104 includes a processor module 124, a memory module 126, and a signal processing module 128. Also included is a wireless channel formed by communication path h₁₁、h₁₂、h₂₂、h₂₁、h_{2 NTX}、h_{1 NTX}、h_{NRX 1}、h_{NRX 2}、h_{NRX NTX}Composition of, here h_mnRepresents the channel coefficients from transmit antenna n to receive antenna m. With N_TXA transmitting antenna and N_RXA receiving antenna. Also shown is a transmit symbol (transmit symbol) x₁、x₂、x_NTXAnd received symbol (received symbol) y₁、y₂、y_NRX。

MIMO transmitter 102 includes enabling generation of transmit symbol x_i(i∈{1，2，...N_TX}) of the memory element may be implemented as suitable logic, circuitry and/or code. The transmitted symbols are transmitted by transmit antennas, of which antennas 106, 108 and 110 are depicted in fig. 1B. The processor module 118 comprises suitable logic, circuitry, and/or code that enables processing of signals. The memory module 120 may comprise suitable logic, circuitry, and/or code that may enable storage and/or retrieval of processing information for the MIMO transmitter 102. The signal processing module 122 may comprise suitable logic, circuitry, and/or code that may enable processing of signals, such as in accordance with one or more MIMO transmission protocols. MIMO receiver 104 includes enabling processing of received symbols y_i(i∈{1，2，…N_RX) Suitable logic, circuitry and/or code. The received symbols are received by receive antennas, of which antennas 112, 114 and 116 are depicted in fig. 1B. The processor module 124 comprises suitable logic, circuitry, and/or code that enables processing of signals. The storage module 126 includes enabling storage and/or retrieval of processing information for the MIMO receiver 104Suitable logic, circuitry, and/or code. The signal processing module 128 may comprise suitable logic, circuitry, and/or code that may enable processing of signals, such as in accordance with one or more MIMO protocols. The input-output relationship between the transmission signal and the reception signal in the MIMO system is specifically expressed as follows:

y＝Hx+n

here, y ═ y₁，y₂，...y_NRX]^TIs provided with N_RXColumn vector of elements,. T represents a vector transpose matrix, H ═ H_ij](i∈{1，2，...N_RX}；j∈{1，2，...N_TX}) is N_RX*N_TXA channel matrix of dimensions; x ═ x₁，x₂，...x_NTX]^TIs provided with N_TXA column vector of elements. N is N_RXA noise sample column vector of elements.

Fig. 1B is a system diagram illustrating a multi-antenna system applied to a Universal Mobile Telecommunications System (UMTS) Long Term Evolution (LTE) system. Symbol stream passing through N_TXEach of the transmitting antennas transmitting, e.g. symbol x₁(t) is transmitted via antenna 106. A stream of symbols, e.g. x₁(t) comprising one or more symbols, where each symbol is modulated onto a different subcarrier. OFDM systems typically use a relatively large number of parallel subcarriers for each symbol stream. For example, the symbol stream x₁(t) inclusion in carrier f_m: m ∈ {1, 2.. M } (M is a subset of the FFT length used at the receiver). For example, an FFT of length N (N > M) produces guard-tones (guard-tones), which allow variable bandwidth to be used when using, for example, 64, 128 or 512 sub-carriers. M subcarriers comprising a stream of symbols, e.g., x₁(t), the symbol stream may occupy a bandwidth of several kilohertz to several megahertz. For example, typical bandwidths are between 1MHz and 100 MHz. Thus, each symbol stream includes one or more subcarriers for each of which the wireless channel includes multiple transmission paths. For example, as shown in the figure, a wireless channel h from a transmit antenna 108 to a receive antenna 112₁₂Is multi-dimensional. In particular, the radio channel h₁₂Including a temporal impulse response consisting of one or more multipath components. For each subcarrier f of the symbol stream_mOver a radio channel h₁₂It may also include different temporal impulse responses, e.g. x₂(t) of (d). The wireless channel shown in fig. 1B describes the spatial dimensions of the wireless channel, since the transmitted signals from the various transmit antennas may be different when received by each receive antenna, and thus, the channel impulse response may be measured and/or estimated for each subcarrier.

Fig. 2 shows a schematic diagram of an OFDM symbol stream in accordance with an embodiment of the invention. Referring to fig. 2, a time-frequency axis 210, symbol 0, symbol 1 is shown. At frequency f₁Here, symbol 0 includes cyclic prefix CP (0)202a, inverse fourier transform (IFFT) symbol less CP (0) (IFFT (0))202b, and cyclic prefix CP (0)202 c; symbol 1 includes a cyclic prefix CP (1)204a, an inverse fourier transform (IFFT) symbol less CP (1) (IFFT (0))204b, and a cyclic prefix CP (1)204 c. IFFT (0)202b and CP (0)202c together form time domain symbol 0 at frequency f₁One complete IFFT symbol. CP (0)202a is substantially similar to CP (0)202 c. Similarly, IFFT (1)204b and CP (1)204c together make up time-domain symbol 1 at frequency f₁One complete IFFT symbol, and CP (1)204a is actually similar to CP (1)204 c. Similarly, it is also shown that at frequency f₂Here, symbol 0 includes cyclic prefix CP (0)206a, inverse fourier transform (IFFT) symbol less CP (0) (IFFT (0))206b, and cyclic prefix CP (0)206 c; symbol 1 includes a cyclic prefix CP (1)208a, an inverse fourier transform (IFFT) symbol less CP (1) (IFFT (0))208b, and a cyclic prefix CP (1)208 c. Also shown is an FFT input window 214 (shown in dashed lines), a guard time Δ t_gFrequency offset Δ f, slot marker 212. For example, an LTE slot architecture includes 3, 6, or 7 OFDM symbols (2 of which are shown in fig. 2) per slot in the time domain.

To produce an Orthogonal Frequency Division Multiplexing (OFDM) symbol, the output of the IFFT containing IFFT (0)202b and CP (0)202c is used to generate CP (0)202a from CP (0)202 c; and appended to IFFT (0)202 b. The cyclic prefix CP (0)202 is used to avoid inter-symbol interference for OFDM receivers in the presence of multipath propagation for wireless channels.

At the OFDM receiver side, e.g., MIMO receiver 104, for each received symbol, the sampled input signal is processed (e.g., through FFT input window 214). In order to decode the received symbols, the FFT input window 214 also needs to be placed in a time domain symbol slot, e.g., time domain symbol 0. In particular, the FFT input window 214 cannot extend into adjacent symbols to avoid inter-symbol interference. Also, the FFT input window 214 cannot overlap a plurality of symbols in the frequency domain. Then the gap identification marks the beginning of a gap, e.g., time domain symbol gap 0 as shown in fig. 2. Guard time Δ t_gAnd the slot identifier 212 together define the position of the FFT input window 214 in the time domain symbol slot. Similarly, the carrier frequency (e.g. f)₁Or f₂) And the frequency offset deltaf together determine the position of the FFT input window 214 in the frequency domain. In most cases, to reduce interference due to multipath channels as much as possible at the receiver end, it is necessary to make Δ t_gAnd Δ f are small.

Therefore, it is very necessary to acquire frequency and time information and keep track of frequency and time when shifting (e.g., changes in transmission due to movement). In some cases, other frequency and time acquisition and tracking processes are also incorporated. In most cases, coarse synchronization of frequency and time can be performed by a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS). Fine tracking of frequency and time is obtained by a frequency acquisition and tracking system that may use Reference Symbols (RSs) embedded in the OFDM signal. The reference symbols may be known symbols that are transmitted over time, frequency, and spatial resources in the OFDM system according to a known pattern. In other words, reference symbols may be transmitted at known times over known OFDM carriers via certain antennas. The receiver determines the correct time and frequency information by decoding and processing the RS symbols, e.g., by coherent demodulation (coherent demodulation). RS symbols may be transmitted from each antenna of a multi-antenna OFDM system.

In an Evolved Universal Terrestrial Radio Access (EUTRA) interface, RS symbols are generated based on a cell-specific hopping pattern and are composed of a pseudo-noise (PN) covered (covered) sequence of reference symbols. In accordance with one embodiment of the present invention, the RS tone spacing (tone spacing) is 6 carriers, e.g., per transmit antenna. According to various embodiments of the present invention, the RS tone spacing (tone spacing) is, for example, 2 or 4 carriers. The RS sequence is not known to the mobile terminal (user equipment, UE) in the initial acquisition (e.g. by the synchronization signal). In some cases, after acquiring a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS), the UE acquires a cell-specific hopping pattern and PN coverage sequence for the RS symbol. This information can be used to obtain coarse frequency and time information. The RS symbols are then decoded by one or more frequency and time acquisition and tracking modules to provide fine frequency and time tracking, in accordance with various embodiments of the present invention.

Fig. 3 is an exemplary OFDM frequency and time acquisition and tracking system in accordance with an embodiment of the present invention. Referring to fig. 3, a common receiver portion 342, a frequency and time portion 340 are shown. The frequency and time section 340 includes an RS error block (error block)302, an RS time and frequency loop (loop) 304. Also shown are the RS set input, the frequency error signal f_kTime error signal e_kAn output signal txco _ accum and an output signal to _ accum. The general receiver portion 342 includes a time generator 312, an RS extraction module or circuit 314, a channel estimation module 316, a receiver operation module (RXCVR)318, a Fast Fourier Transform (FFT) module 320, a buffering module 330, a sampling Bandwidth (BW) filter 332, an analog-to-digital conversion module 334, a master clock 336, a temperature controlled crystal oscillator (TXCO) 338. Also shown are the RF filter input, the master clock input, the gap clock input from the PSS, the RS set output, the txco _ accum signal, the to _ accum signal, the RS _ strb signal, the slot _ strb signal.

The frequency and time portion 340 includes enabling pass throughAppropriate logic, circuitry, and/or code to process a set of RS signals that produce, for example, an output TXCO _ accum that controls TXCO338 to extract frequency and time information from the received OFDM signal. In addition, the frequency and time section 340 can generate an output signal to _ accum, for example, for controlling the system time by the time generator 312. The RS error module 302 includes enabling tracking of frequency and time offset (e.g., Δ t as shown in FIG. 2)_gAnd Δ f) and suitable logic, circuitry, and/or code.

The general receiver portion 342 may comprise suitable logic, circuitry, and/or code that may enable receiving radio frequency signals and processing such signals. The processing here includes FFT computation, RS symbol extraction, channel estimation and other receiver signal processing. The time generator 312 comprises suitable logic, circuitry, and/or code that enables the generation of a time signal for RS extraction of RS _ strb and the gap time slot _ strb. The signal slot _ strb is used to control, for example, the FFT time and frequency in the buffer block 330. The block or circuit 314 may comprise suitable logic, circuitry, and/or code that may enable extraction of an RS symbol from the output of the FFT block or circuit 320.

The channel estimation module or circuitry 316 may comprise suitable logic, circuitry and/or code that may enable estimation of the wireless channel response of the RS symbol, as may be appropriate for receiver operation. The receiver operation module or circuit (RXCVR)318 comprises suitable logic, circuitry, and/or code that enables performance to be measured and/or verified while the receiver is operating. The Fast Fourier Transform (FFT) block or circuit 320 may comprise suitable logic, circuitry, and/or code that may enable a fast fourier transform to be generated on an input signal. The buffer module or circuitry 330 may comprise suitable logic, circuitry, and/or code that may enable interfacing with, for example, an FFT engine. The buffer module or circuit 330 may be configured to facilitate dedicated processing, measurement processing, Multimedia Broadcast and Multicast Service (MBMS), and/or SSS processing for hopping pattern determination. In some cases, each process may be performed in parallel.

The sample bandwidth (bandwidth) filter 332 may comprise suitable logic, circuitry, and/or code that may enable filtering of an input signal and generation of a bandwidth limited output signal. The analog-to-digital conversion (A2D) block or circuit 334 may comprise suitable logic, circuitry, and/or code that may enable receiving an analog filtered radio frequency signal and converting it at an output to a digital signal representation of any number of bits. The master clock 336 may comprise suitable logic, circuitry, and/or code that may enable the provision of basic time and/or frequency functions in a receiver. In some cases, master clock 336 is clocked at a 10ms period, such as at a clock frequency of 30.72 MHz. The master counter includes a gap counter and a sampling counter. TXCO338 comprises suitable logic, circuitry, and/or code that enables the generation of output signals of different frequencies, the output signals (e.g., voltages) being a function of the input signals.

The general receiver portion 342 receives and processes radio frequency signals. The processing here includes FFT computation, RS symbol extraction, channel estimation and other receiver signal processing. Some of the frequency and/or time characteristics of the general receiver portion 342 are controlled by the frequency and time portion 340. For example, the receiver subcarrier/carrier frequency (e.g., f1 and/or f2 shown in fig. 2) is determined by TXCO 338. Similarly, time is controlled by the time generator 312 via the to _ accum signal.

The RS error module 302 is used to compare the frequency and time of an RS set input (set input) signal with, for example, an input clock signal and generate a frequency error signal f_kAnd a time error signal e_k. The RS error module 302 receives at an input the set of RS symbols extracted by the RS extraction module 314. The output of the RS error module 302 is communicatively coupled to an RS time and frequency loop 304.

The RS time and frequency loop 304 tracks time and frequency offsets, e.g., Δ t as shown in FIG. 2_gAnd Δ f. The RS time and frequency loop 304 can generate a time output signal to _ accum (this output signal is Δ t)_gA function of) and a frequency output signal txco _ accum (which is a function of Δ f). According to one embodiment of the invention, the TXCO _ accum signal increases at a rate that is a function of Δ f, thus allowing information about Δ f to be passed to, for example, TXCO338 and used to control the position of the FFT input window in the frequency domain. Similarly, the to _ accum signal is given at Δ t_gIs increased, thus allowingRelated to Δ t_gIs passed to, for example, a time generator 312 and is used to control the position of the FFT input window in the time domain.

An analog-to-digital conversion (A2D) module or circuit 334 receives the analog Radio Frequency (RF) filtered signal and converts it at an output to a digital signal representation of any number of bits. The A2D 334 output is communicatively coupled to sampling BW filter 332. The sampling BW filter 332 filters the input signal to produce a limited bandwidth output signal and/or to attenuate certain frequency bands (frequency bands). The output of the sampling BW filter 332 is communicatively connected to a first input of a buffer module or circuit 330. A second input of the buffer block or circuit 330 is communicatively coupled to the slot _ strb terminal of the output signal of the time generator 312. The buffer module or circuit 330 facilitates dedicated processing, measurement processing, Multimedia Broadcast and Multicast Service (MBMS), and/or SSS processing for RS PN sequence determination. In some cases, each process may be performed in parallel. The output of the buffer module or circuit 330 is communicatively coupled to the FFT module or circuit 320.

The FFT block or circuit 320 performs a fast fourier transform on the input signal from the buffer block or circuit 330. Similar to the buffer module or circuit 330, the FFT module or circuit 320 facilitates dedicated processing, metric processing, Multimedia Broadcast and Multicast Service (MBMS), and/or SSS processing for radio time frame and RS PN sequence determination. The output of the buffer module or circuit 330 is communicatively coupled to the FFT module or circuit 320. A first output of the FFT module or circuit 320 is communicatively coupled to a first input of the RS extraction module or circuit 314. The RS extraction module or circuit 314 extracts the RS symbols from the output of the FFT module or circuit 320. In some cases, it may be appropriate to use the generated hopping sequence from the demodulated base station signal and/or Pseudo Noise (PN) covering the RS decoding. The extracted RS symbols and the output of the RS extraction module or circuit 314 are delivered to the frequency and time section 340 and to the input of the channel estimation module or circuit 316. As shown in fig. 3, the transition pattern is transmitted to the RS extraction module or circuit 314 through the second input signal RS _ hopping _ pattern. The timing of the RS extraction block or circuit 314 is controlled by a third input signal RS _ strb from the timing generator 312.

The time generator 312 generates time and frequency signals for the RS extraction RS _ strb and the gap time slot _ strb. The signal slot _ strb is used to control the FFT time and frequency of the buffer block or circuit 330. The time generator 312 generates an output inter-toggle signal from a function of the master clock input signal, the gap time (PSS), to enable time and frequency correction and tracking. The master clock input signal may be transmitted to an output of master clock 336. The master clock 336 provides the reference time and frequency functions of the receiver. In some cases, the master clock 336 counts in 10ms periods, for example, at a clock frequency of 30.72 MHz. The master counter includes a gap counter and a sampling counter. The input to the master clock 336 is provided by an operating RF crystal, such as a temperature controlled crystal oscillator (TXCO) 338. The TXCO338 is communicatively coupled to a threshold module or circuit 310 via a TXCO _ accum signal.

The channel estimation module or circuit 316 is used to estimate the wireless channel response of the RS symbols, as appropriate for receiver operation. The output of the channel estimate is communicatively coupled to RXCVR 318. RXCVR 318 is used to measure and/or verify the performance of the receiver.

Fig. 4 is a flow diagram of an exemplary frequency and time acquisition and tracking in accordance with an embodiment of the present invention. After start step 402, the primary synchronization signal PSS and secondary synchronization signal SSS are decoded separately in step 404. Decoding of PSS and SSS provides coarse frequency and time information for frame and slot synchronization. For example, the FFT module 320 generates an FFT of the received signal using the frequency and time information. For example, the RS extraction module 314 extracts the set of RSs in the RS extraction module 314 using the generated FFT. This set of RSs communicates with frequency and time portion 340.

In step 408, the frequency and time portion 340 tracks the frequency offset Δ f and the time offset Δ t using the RS time and frequency loop 304 (shown in FIG. 3)_g. Since the TXCO _ accum output signal generated is a function of Δ f, the TXCO _ accum output signal from the threshold module 310 passes information about Δ f to the TXCO 338. Similarly, for example, the generated output signal to _ accum is Δ t_gWith respect to Δ t_gIs sent to the time generator 312. Thus, the output signals TXCO _ accum and to _ accum can track the carrier frequency and time and adjust the receiver frequency and time in the master clock 336 through the TXCO338 and time generator 312. In step 410, the master clock 336 adjusts the frequency based on the input signal txco _ accum and the time generator 312 adjusts the FFT input window time.

In accordance with embodiments of the present invention, a method and system for joint time and frequency tracking for OFDM includes tracking carrier frequencies and symbol times of an orthogonal frequency division multiplexed signal based on at least one reference symbol set (e.g., as shown in fig. 2). The receiver frequency and time are adjusted based on the tracked carrier frequency and symbol time.

The carrier frequency is tracked by generating an output signal as a function of the frequency offset af. By generating a guard time Δ t_gThe output signal of the function to track the symbol time. As shown in fig. 2 and 3, the received OFDM signal is fast fourier transformed to generate a set of Reference Symbols (RSs). The receiver frequency and time are fine-tuned after a coarse tuning. As shown in fig. 4, the coarse receiver frequency and time adjustment is based on the processing of the primary and secondary synchronization signals. The reference symbol set includes a plurality of time-frequency gaps, which may vary according to a hopping pattern determined by a base station identifier. The OFDM signal conforms to the Long Term Evolution (LTE) signal standard of the Universal Mobile Telecommunications Standard (UMTS). For example, the adjustment of the receiver frequency is controlled by a receiver frequency oscillator (TXCO)338 and the adjustment of the time is controlled by a time generator 312.

Another embodiment of the present invention provides a machine-readable and/or computer-readable storage and/or medium, having stored thereon, a machine code and/or a computer program having at least one code section executable by a machine and/or a computer, thereby causing the machine and/or computer to perform the steps of the OFDM joint time frequency tracking system described herein.

Accordingly, the present invention may be realized in hardware, software, or a combination of both. The present invention can be realized in a centralized fashion in at least one computer system, or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system or other apparatus adapted for carrying out the methods described herein is suited. A typical combination of hardware and software could be a general purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods described herein.

The present invention can be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which, when loaded in a computer system is able to carry out these methods. Computer programming in the present context may be any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: a) conversion to another language, code or notation; b) reproduced in a different material form.

While the invention has been described with reference to specific embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A method of processing a communication signal, the method comprising:

receiving an analog radio frequency filtering orthogonal frequency division multiplexing signal;

an analog-to-digital conversion module (334) converts the analog radio frequency filtered orthogonal frequency division multiplexing signal into a digital signal;

a sampling bandwidth filter (332) filters the digital signal;

a buffering module (330) buffers the filtered signal;

a fast Fourier transform module (320) performs fast Fourier transform on the buffered signal from the buffering module to generate a fast Fourier transform signal;

a reference symbol extraction module (314) extracts at least one set of reference symbols from the generated fast fourier transform signal;

a channel estimation module (316) estimates a wireless channel response of the extracted at least one reference symbol set;

a frequency and time section (340) tracks a carrier frequency and a symbol time of the orthogonal frequency division multiplexing signal based on the extracted at least one reference symbol set;

the outputs of the channel estimation module (316) and the fast fourier transform module (320) are both communicatively coupled to a receiver operation module (318), the receiver operation module (318) measuring and/or verifying the performance of the receiver;

an output of the receiver frequency oscillator (338) is connected to the master clock (336), an output of the master clock (336) is connected to the time generator (312), the receiver frequency oscillator (338) and the time generator (312) adjust a frequency and a time of the receiver based on the tracked carrier frequency and symbol time; and

the time generator (312) controls the fast fourier transform time and frequency of the buffer module (330);

the time generator (312) also provides the time of the reference symbol extraction module (314).

2. The method of processing a communication signal of claim 1, wherein the set of reference symbols comprises a plurality of time-frequency slots, the method further comprising:

the plurality of time-frequency gaps vary as a function of time-frequency drift and a pseudo-noise sequence used to modulate the set of reference symbols.

3. The method of processing a communication signal according to claim 1, further comprising tracking the carrier frequency by generating an output signal as a function of frequency offset af.

4. The method of processing a communication signal according to claim 1, further comprising generating a guard time Δ t as the one_gThe output signal of the function to track the symbol time.

5. The method of processing a communication signal of claim 1, further comprising fine tuning a frequency and a time of the receiver.

6. The method of processing a communication signal of claim 5, further comprising, prior to the fine adjustment, coarsely adjusting the frequency and time of the receiver.

7. The method of processing a communication signal of claim 6, further comprising generating a coarse adjustment of the receiver frequency and time based on processing of a primary synchronization signal and a secondary synchronization signal.

8. A system for processing a communication signal, comprising:

an analog-to-digital conversion module (334) for receiving an analog radio frequency filtered orthogonal frequency division multiplexing signal and converting the analog radio frequency filtered orthogonal frequency division multiplexing signal into a digital signal;

a sampling bandwidth filter (332) for filtering the digital signal;

a buffering module (330) for buffering the filtered signal;

a fast Fourier transform module (320) for performing a fast Fourier transform on the buffered signal from the buffering module to generate a fast Fourier transform signal;

a reference symbol extraction module (314) for extracting at least one set of reference symbols from the generated fast fourier transform signal;

a channel estimation module (316) for estimating a wireless channel response of the extracted at least one reference symbol set;

a frequency and time section (340) for tracking a carrier frequency and a symbol time of the orthogonal frequency division multiplexing signal based on the extracted at least one reference symbol set;

a receiver operation module (318) for measuring and/or verifying the performance of the receiver;

the time generator (312) is further configured to control a fast fourier transform time and frequency of a buffer module (330);

the time generator (312) is further configured to provide a time for a reference symbol extraction module (314); wherein

The outputs of the channel estimation module (316) and the fast fourier transform module (320) are communicatively coupled to a receiver operation module (318).

9. The system for processing a communication signal according to claim 8, wherein said frequency and time portion (340) comprises a reference symbol time and frequency loop (304) for tracking said carrier frequency by generating an output signal as a function of a frequency offset af.

10. The system for processing a communication signal according to claim 8, wherein said frequency and time portion (340) comprises a reference symbol time and frequency loop (304) for generating a guard time Δ t by generating a guard time Δ t_gThe output signal of the function to track the symbol time.