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IMPROVED SLOT SYNCHRONIZATION SCHEME FOR APC02fi SLOTTED ALOHA

IP.com Disclosure Number: IPCOM000008860D
Original Publication Date: 1998-Sep-01
Included in the Prior Art Database: 2002-Jul-18
Document File: 2 page(s) / 105K

Publishing Venue

Motorola

Related People

Robert Rzepiela: AUTHOR [+3]

Abstract

INTRODUCTION Before transmitting on an APCO-25 trunked system, Subscriber Units (SU) must acquire frame synchronization and slot synchronization. Slot syn- chronization consists of obtaining the slot size and boundary locations of the control channel. This is a time consuming process which directly effects the Trunking System Access equation, which is used to specify system performance. From a performance standpoint, it is best to minimize the slot synchro- nization time. Currently, it is estimated that the slot synchronization procedure within Motorola Subscriber Units will account for approximately 70% of the total control channel lock time.

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MO7WROLA Technical Developments

IMPROVED SLOT SYNCHRONIZATION SCHEME FOR APC02fi

SLO-ITED ALOHA

by Robert Rzepiela, Michael L. Johnson and Robert Biggs INTRODUCTION

  Before transmitting on an APCO-25 trunked system, Subscriber Units (SU) must acquire frame synchronization and slot synchronization. Slot syn- chronization consists of obtaining the slot size and boundary locations of the control channel. This is a time consuming process which directly effects the Trunking System Access equation, which is used to specify system performance. From a performance standpoint, it is best to minimize the slot synchro- nization time. Currently, it is estimated that the slot synchronization procedure within Motorola Subscriber Units will account for approximately 70% of the total control channel lock time. BACKGROUND

  The SU may need to lock to a control channel for a variety of reasons. These include initial con- trol channel acquisition on power up, the loss of control channel during failure conditions or when roaming from one site to another. The time to lock to the control channel on the APCO-25 compliant

system depends on the control channel format and slot size. APCO specifies single, dual and triple TSBK control channel formats and allows manufac- turers of the infrastructure to select any control channel format and size.

  In majority of cases, the time for the SU to lock to a control channel is composed of hardware, soft- ware and protocol dependent delays. The first two items add up to approximately 23 msec (average time) for a Motorola SU. In an APCO-25 system, obtaining Frame Synchronization and Network ID (NID) will take additional time (Tee-format). Assuming uniform and random distribution, this time is 18.75, 30 and 37.5 msec for single, dual and triple TSBKs control channel format, respectively.

  The time to acquire slot synchronization using standard techniques ranges from 100 to 120 msec for a slot size of 45 msec. The time to obtain slot sync is linear function of slot size and therefore only a 45 msec slot size will be considered here. Figure 1 below presents the data.

Fig. 1 Slot Sync Impact on Control Channel Lock (2%...