Pulse or digital communications – Transceivers
Reexamination Certificate
1998-09-30
2003-11-04
Pham, Chi (Department: 2631)
Pulse or digital communications
Transceivers
C375S295000, C375S373000
Reexamination Certificate
active
06643321
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a method for rapid synchronization of a point to multipoint modem system and, in particular, to a method for increasing the efficiency of processing of a received signal by storing the carrier frequency offset and equalizer taps between processing of burst transmissions.
Many different types of communication systems feature a master modem, at a base station, which then controls the transmissions of a plurality of slave modems, at terminal stations. For example, such a communication system is often used for wireless communication according to a TDM (time division multiplexing) protocol, an FDD (frequency division duplex) protocol and a TDMA (time division multiple access) protocol. Transmission from the base station to the terminal stations for the downstream transmissions is performed at one carrier frequency, and transmissions from the terminal stations to the base station, or upstream transmissions, are performed at another frequency, such that the downstream and upstream transmissions do not interfere with each other. For upstream transmissions from the terminal stations to the base station, communication follows the TDMA protocol. Downstream transmissions, however, are continuous and are performed according to the TDM protocol, for example. The base station determines the timing of transmissions by the terminal stations. In order for communication to occur, a transmitted signal must be accurately processed by the receiver for accurate recovery of the information contained within the signal.
For example, radio frequency signals are subject to distortion such as amplitude and phase distortion, carrier frequency offset and phase noise. Amplitude and phase distortion, which cause time dispersion, are known as channel response. The transmission frame may include synchronization fields, which are required for correct processing of the frame to overcome the above-mentioned distortions, yet which must be minimized in order to maximize the available bandwidth. In the upstream direction, due to the bursty nature of the transmission, every burst must include synchronization fields. For example, these fields may appear at the beginning of the burst, and then they form the header. When bursts are relatively short, the synchronization overhead must be decreased as much as possible, such that the synchronization fields must be as short as is practical.
One typical approach to compensate for channel response (amplitude and phase distortion and time dispersion of the signal) in a receiver is an equalizer. The equalizer includes a plurality of “taps”, each of which has an associated equalizer coefficient, with a delay separating each tap. The equalizer coefficients may be calculated using an iterative approach, where the coefficients are adjusted until the coefficients converge acccording to some algorithm, such as LMS (least mean squares) (see for example chapter 6 of
Adaptive Signal Processing
, by. B. Widrow and S. D. Stearns, Prentice-Hall, Inc., Englewood Cliffs, N.J., USA, 1985). Since the channel response is typically time variant for wireless communication, equalizers are usually adaptive, such that the equalizer coefficients are varied over time to be able to track the changes in the channel response. The rate at which the equalizer coefficients are adjusted depends upon the rate at which the channel response varies over time. Typically for background art equalizers for wireless communication according to TDMA, the equalizer coefficients are adjusted for each burst alone, without reference to any previous burst, which requires longer synchronization fields and lengthier calculations.
One example of a system which attempts to increase the speed for signal processing is disclosed in U.S. Pat. No. 4,847,880. The disclosed system stores certain equalizer coefficients for one initial training session, and then uses these stored coefficients for all subsequent equalizations of the signal. The equalizer coefficients are not updated at any later time. This approach is only suitable for a channel which is not varying. Thus, the storage of these coefficients is used to increase the efficiency of processing, but is inoperative for a time varying channel, such as for wireless communication.
However, for certain types of applications, in particular fixed systems in which both the base station and the terminal stations are stationary, various values calculated during the signal processing change relatively slowly between consecutive bursts, but these values are still time variant. For example, the equalizer coefficients typically do not change significantly between bursts. Therefore, using the values obtained from the calculation of equalizer coefficients for a previous burst transmission as the basis for the calculation for a subsequent consecutive burst from the same terminal station, rather than starting from a random or otherwise unrelated value, could significantly improve the efficiency of the equalizer coefficient adaptation. Unfortunately, no currently available system takes advantage of those receiver parameters which change relatively slowly.
There is thus a widely recognized need for, and it would be highly advantageous to have, a system and a method for storing certain relatively slowly changing receiver parameters between transmissions for signal processing, such as the equalizer coefficients and the carrier frequency offset, in order to increase the efficiency of signal processing, and decrease the length of synchronization fields, thereby maximizing available bandwidth.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a system for communication between a base station and at least one terminal station, the base station receiving a plurality of sequentially transmitted bursts from the at least one terminal station according to a TDMA (time division multiple access) protocol, each burst featuring a synchronization portion, each of the plurality of sequentially transmitted bursts being denoted S
i
wherein i is an integer, the plurality of sequentially transmitted bursts including at least a burst S
m
and a burst S
n
being sent from one terminal station, wherein m and n are each integers and m<n, the system comprising: a base station transceiver comprising: (i) a receiver unit for receiving the plurality of bursts S
i
, including at least the burst S
m
and the burst S
n
, and for producing each of a plurality of analog signals from each of the plurality of bursts S
i
; (ii) an analog-to-digital converter for converting each analog signal to a sampled digital signal, by sampling each analog signal according to a sampling timing; (iii) an adaptive equalizer for equalizing each sampled digital signal according to each of a plurality of sets of equalizer coefficients to produce an equalized signal, such that a sampled digital signal corresponding to a particular burst S
i
is equalized according to a particular set of equalizer coefficients; and (iv) an equalizer controller for determining each set of coefficients by processing a portion of an equalized signal corresponding to the synchronization portion of a burst S
i
according to an initialized coefficient adjustment procedure; such that for processing a portion of an equalized signal corresponding to the synchronization portion of the burst S
n
, the initialized coefficient adjustment procedure is initialized by adapting a set of coefficients at least partially determined by processing a portion of an equalized signal corresponding to the synchronization portion of the burst S
m
.
Preferably, n=m+1 and the equalized signal corresponding to the burst S
n
is equalized according to the set of coefficients produced by processing the portion of the equalized signal corresponding to the synchronization portion of the burst S
n
.
Alternatively and preferably, the plurality of bursts S
i
includes a burst S
q
, q being an integer and q>n, and an equalized signal corresponding to the burst S
q
is equalized according to
Chayat Naftali
Genossar Michael Joshua
Gotman Max
Mizrahi Natan
Alvarion Ltd.
Friedman Mark M.
Kumar Pankaj
Pham Chi
LandOfFree
Method for rapid synchronization of a point to multipoint... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for rapid synchronization of a point to multipoint..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for rapid synchronization of a point to multipoint... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3175871