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A MAXIMAL-RATIO TIME DIVERSITY DATA DECODER

IP.com Disclosure Number: IPCOM000007289D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2002-Mar-12
Document File: 5 page(s) / 326K

Publishing Venue

Motorola

Related People

Brad Hiben: AUTHOR [+3]

Abstract

Range and efficiency are important measures of radio data system performance. Normally, range is improved by use of stronger forward error correc- tion codes. This degrades the efficiency of the radio data system because more system capacity is devoted to parity information for the stronger error correc- tion codes. Efficiency can be improved by using higher rate, i.e., weaker, error correction codes and accepting a decrease in the coverage range. This invention uses maximal-ratio time diversity to simultaneously improve the efficiency and coverage range obtainable in a radio data system.

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MOmOLA Technical Developments Volume 23 October 1994

A MAXIMAL-RATIO TIME DIVERSITY DATA DECODER

by Brad Hiben, Don Newberg and James Butler

increase the probability ofsuccessful message trans- fer. Typically, the data message is retransmitted if acknowledgment of successful transfer is not received within a certain time period. This is a type of time diversity. But it is sub optimal diversity from the standpoint that there is no processing gain derived from having transmitted the message multiple times. Each retransmission is processed independently and thus has the same probability of success as the ini- tial transmission. This invention teaches a method by which successive transmissions are combined using the maximal-ratio technique in order to obtain a successively increasing probability of succes.&l mes- sage transfer with each retransmission.

  It is important that the various linear combina- tions of received signals arrive at the maximal-ratio combiner with differential delays that are small com- pared to the modulation component ofthe signal. If the differential delays are too large, simulcast distor- tion will be generated inside the maximal-ratio combiner itself, In the C4FM digital systems, the various signals must arrive at the combiner within *5 PS of each other or an irreducible error floor of about 0.5% bit error rate will result. Therefore, this invention includes a method and apparatus for prop- erly aligning the data message transmissions that arrive at different times.

  Figure 1 is a block diagram of the receiver sec- tion of a standard data radio. The receiver shown is a digitally implemented receiver which is the cur- rent state of the art. A typical receiver of this type uses an RF A/D converter which produces complex I-Q samples at zero IF The samples are filtered by the IF filter, which may be a digital finite impulse response filter, and applied to a digitally implemented discriminator. The output of the discriminator is baseband real samples. The Bit Recovery block recov- ers the digital bit stream from the post-discriminator baseband sample stream. The frame sync algorithm detects and locates the center of the first symbol in the received data message and provides the initial

BACKGROUND

  Range and efficiency are important measures of radio data system performance. Normally, range is improved by use of stronger forward error correc- tion codes. This degrades the efficiency of the radio data system because more system capacity is devoted to parity information for the stronger error correc- tion codes. Efficiency can be improved by using higher rate, i.e., weaker, error correction codes and accepting a decrease in the coverage range. This invention uses maximal-ratio time diversity to simultaneously improve the efficiency and coverage range obtainable in a radio data system.

DESCRIPTION OF SOLUTION

  Maximal-ratio combining is a technique which co-phases the signals from multiple sources, scales their magnitudes...