Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

AN ADAPTIVE METHOD FOR THE EXTRACTION OF CHANNEL IMPAIRMENTS FROM A DIGITAL SYNCHRONIZATION PATTERN

IP.com Disclosure Number: IPCOM000009419D
Original Publication Date: 1999-Sep-01
Included in the Prior Art Database: 2002-Aug-22
Document File: 4 page(s) / 171K

Publishing Venue

Motorola

Related People

Kevin Doberstein: AUTHOR

Abstract

In digital modulation schemes, such as with the APCO Project 25 specified modulations CQPSK and C4M, a receiver must be able to synchronize to a transmitted waveform. Unfortunately, various impairments induced by inaccuracies in transmitters and also the RF channel cause degradations in the received synchronization pattern. It is the responsi- bility of the receiver to acquire synchronization under these conditions and after synchronization is acquired, it is also the receiver's responsibility to estimate several parameters required to recover the data. These parameters include the amount of cani- er offset, the amount of gain in the symbols, and the position of the symbol center in the received waveform.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 46% of the total text.

Page 1 of 4

Developments Technical 0 M MOTOROLA

AN ADAPTIVE METHOD FOR THE EXTRACTION OF CHANNEL IMPAIRMENTS FROM A DIGITAL SYNCHRONIZATION PATTERN

by Kevin Doberstein

  In digital modulation schemes, such as with the APCO Project 25 specified modulations CQPSK and C4M, a receiver must be able to synchronize to a transmitted waveform. Unfortunately, various impairments induced by inaccuracies in transmitters and also the RF channel cause degradations in the received synchronization pattern. It is the responsi- bility of the receiver to acquire synchronization under these conditions and after synchronization is acquired, it is also the receiver's responsibility to estimate several parameters required to recover the data. These parameters include the amount of cani- er offset, the amount of gain in the symbols, and the position of the symbol center in the received waveform.

  Synchronization is typically done in the receiver by cross-correlating the received waveform with the

expected synchronization pattern and looking for a high degree of correlation.

  The estimation of the amount of carrier offset is done by averaging the amount of dc offset in the received waveform at the known symbol centers and subtracting off the inherent dc offset in the synchro- nization pattern.

   The amount of gain in the symbols and the position of the symbol center in the received wave- form is determined by the magnitude of the correla- tion peak and the location of the correlation peak respectively. Since the synchronization pattern is relatively short, the random interference added may not always be canceled out by the current estimation techniques causing errors in the parameters being estimated.

0 Motomla. 1°C. 1999

360 400 420 440 sample number symbols OUtSide VSA

Fig. 1

18 September 1999

[This page contains 15 pictures or other non-text objects]

Page 2 of 4

Developments Technical 0 M MOTOROLA

  This invention performs the parameter estima- tion process in an adaptive manner, that is it makes use of the apriori knowledge of the sync pattern when the time comes to compute the DC netting error and deviation of the received sync pattern. The fact that we "know" what pattern we are expecting is exploited. Only symbols that would not have pro- duced a bit error are used in the DC netting error estimation and deviation estimations. This allows a better estimation of these parameters even in the presence of noise and fading.

  Figure 1 shows two received sync patterns for an APCO-25 compliant receiver. The APCO-25 sync is

described in the APCO Common Air Interface docu- ment and is a 24 symbol pattern that is comprised solely of +3 (0.18 on the baseband scale) and -3 (-
0.18) symbols. One curve, indicated by Sync at 0% BER, is the received sync pattern under strong sig- nal conditions. The second curve is the same signal only this time the signal conditions are such that the BER is at a 5% level. Superimposed on the curves is the predicted symbol center for each of the 24 symb...