By: Anjaneya Datla

What are TDMA Systems? Time division multiple access (TDMA) is a channel access method for shared medium networks. Several users can share the same frequency channel by dividing the signal into different time slots.

TDMA Frame Structure

Introduction (continued) The users transmit in rapid succession, one after the other, each using its own time slot. Multiple stations can share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity with this technique. TDMA is implemented in: 2G cellular systems like GSM,IS-136,Personal digital cellular, etc.

Scenario in a TDMA System A single base station failure in TDMA wireless systems causes all active calls on this base station to be dropped. In order to increase system end-to-end availability,a multiple channel recovery method for TDMA wireless systems is required. when a base repeater fails, the channels of active calls carried by the base station are replaced by working channels in the channel pool of the base site.

Continued The method deals not only with the failure and recovery of base stations, but also with the channel failure recovery in handoff processes, transient channel failures, and new call setup processes. All the active calls continue without the intervention of end users.

Description of the process In wireless communications systems, the base site controller (BSC) handles radio channel allocation and many other functions. Whenever a channel fails, the call carried by the channel will be dropped. There different reasons for a channel failure. We classify these into 2 types: Permanent and transient channel failures.

Description(Continued) The permanent channel failures are caused by equipment failures of base stations, such as power failure or RF amplifier failure, etc. For example: While there are some ongoing calls on the BR, the BR is down. The transient channel failures are caused by many factors in the RF transmission, such as fading, shadowing and interference.

Things Involved The channel recovery method is mainly composed of three processes: 1.Monitoring process, 2.Channel allocation process, 3.BS failure handling process. In order to detect and handle base repeater failures, a base repeater monitoring process is developed. The following slide shows the picture of it.

Monitoring Process Flow Diagram:

Channel Allocation Process The Radio Frequency Channel Allocation consists of various steps. 1. Handling a New Call Requirement. 2. Handling a Hand-off Call. 3. Handling Base-Station Failure. 4. Handling transient failures. 5. Updating Base Station repair status.

Channel Allocation Process Flow Diagram:

Base Station Failure Handling Process: It involves 2 steps: 1. Procedure to update system parameters when a BR repair is completed. 2. Procedure to handle a BR failure handling requirement.

Base Station Failure Handling Process Flow Diagram:

Final Comments The major advantage that we get is reduced percentage of Dropped calls. Using this method we get increased system end –to- end availability.

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