Specifications

ManualsBrandsMotorola ManualsTelephoneiDEN

Interface Protocols

Operating Characteristics

August 08, 2000 68P81095E55-E 3-9

Timeslot Allocation A typical iDEN option increases radio link timeslots allocated to a single voice

conversation for interconnect calls from 1 to 2 per frame. By doubling the timeslots

available, the voice sampling rate can be increased. An increase the voice sample

rate results in improved audio quality. The voice bits are transmitted using two

timeslots of the 6 timeslot frame. This allows the use of the 8.0 kbs VSELP vocoder,

which increases the voice sampling rate to improve tone and richness. The iDEN

system also uses forward error correction to reduce corrupted bits in the voice

transmissions. This results in improved audio quality even in weak signal and

interference areas. This 3:1 interleave is used in interconnect calls.

Figure 3-6 Voice Packet Interleaving

Doubling the number of timeslots per call reduces the traffic carrying capacity of the

system. The timeslot allocation methods provides flexibility for the operator to

balance the requirements for superior audio quality against a reduction in capacity

and support for other services. The breakdown on 3:1 interleave voice channels is:

• Embedded signalling = 0.533333 kbps (24 bits per slot)

• FEC = 6.755555 kbps (304 bits per slot)

• Voice = 8 kbps (360 bits per slot)

• Total = 15.28888 kbps

Both 3:1 and 6:1 voice channels use the same transmission unit defined in the

Layer 2 RF Interface protocol. The main difference is that 3:1 interleave slots arrive

twice as often as 6:1 interleave slots. The method used will affect RF optimization

and planning.

Time Division

Duplex

To further optimize resources, the discrete timeslots in conversation are divided and

offset so transmit (Tx) and receive (Rx) control and voice information can share

resources. Both the uplink to the network and the downlink to the mobile can share

timelsots during interconnect calls. Interconnect calls use two carriers. The Mobile

Transmit and Receive frequencies are separate. With Time Division Duplex the

mobile dynamically shifts frequencies to send and receive voice, data and signalling

information.

VSELP

90ms

Spoken Word

Analog to Digital Conversion

Data

Compression

1 2 3 4 5 6 1 2 3 4 5 6

Enhanced

Interconnect

3:1 Interleave

Two timeslots per call

(Improved Voice Quality)

One timeslot per call

(Conserves resources)

Dispatch/

Interconnect

6:1 interleave

Radio Link timeslots

(15ms slots mimics DS0)

1 2 3 4 5 6 1 2 3 4 5 6

15ms