Browse Prior Art Database

MOBILE-TO-MOBILE HANDOVER ESTIMATION FOR OPTIMAL AUDIO DELAY

IP.com Disclosure Number: IPCOM000009533D
Original Publication Date: 1999-Sep-01
Included in the Prior Art Database: 2002-Aug-30
Document File: 6 page(s) / 204K

Publishing Venue

Motorola

Related People

Michael Kloos: AUTHOR [+2]

Abstract

In order to eliminate the negative effects of tar- dem vocoding (increased delay and degraded audio), iDEN uses a protocol to bypass the vocoders in the infrastructure so that compressed VSELP audio is passed between the transcoders (XCDR) instead of PCM. The result is that a virtual point-to- point connection between the two BR's is created. The JITA algorithm is used within the iDEN system to reduce outbound delay for land to mobile calls. This is accomplished by having the BR send a cor- rection value to the XCDR so it can delay its encoder timing (while introducing a discontinuity) so packets are sent to the BR "Just in Time).

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 50% of the total text.

Page 1 of 6

m MOTOROLA Technical Developments

MOBILE-TO-MOBILE HANDOVER ESTIMATION FOR OPTIMAL AUDIO DELAY

by Michael Kloos and Michael Bychowsky

INTRODUCTION

  In order to eliminate the negative effects of tar- dem vocoding (increased delay and degraded audio), iDEN uses a protocol to bypass the vocoders in the infrastructure so that compressed VSELP audio is passed between the transcoders (XCDR) instead of PCM. The result is that a virtual point-to- point connection between the two BR's is created. The JITA algorithm is used within the iDEN system to reduce outbound delay for land to mobile calls. This is accomplished by having the BR send a cor- rection value to the XCDR so it can delay its encoder timing (while introducing a discontinuity) so packets are sent to the BR "Just in Time).

  By delaying the encoder timing, the packets can be sent to the BR just as it needs it, thus reducing audio delay. This is not possible for mobile-to- mobile calls since the XCDR does not encode the voice but merely passes through the packets encod- ed from the opposite mobile. Instead the XCDR internally delays the packet so that the BR receives the packet just in time for transmission (see Figure
1). The BR does not send any delay request because the timing is correct from the BR perspective, although the delay has not been eliminated in the mobile-to-mobile case, but transferred to the XCDR.

THE PROBLEM

  Each BR inbound stream is encoded just in time for over-the-air transmission for minimal delay. The problem is that this delay cannot be reduced since the over-the-air timeslots are fixed and the Transcoder (XCDR) does not generate packets in the M-M case, the subscriber unit does.

  Because the over-the-air timeslots are chosen without regard for optimal packet timing, there will be, in many cases, some slot combination which would either reduce the delay in both directions, or equalize a short delay in one direction and a long delay in the other direction to some medium delay in both directions, minimizing the longer of the two delays. Also, even if over the air timeslots could be changed, it is not known how to allocate the times- lots to best reduce delay for each call apriori.

  In Figure 1, the current iDEN M-M bypass sce- nario is shown. On each side, the RF slot is chosen by the ACG using the current decision rules. No M- M delay information is used in the slot decision either on call initiation or handover.

0 Mofomla, 1°C. ,999 203 September 1999

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

Page 2 of 6

Developments Technical 0 M MOTOROLA

- =

Switch

/ \*

J...