Specifications

Mobile Computing
Packet Data Networking
August 08, 2000 68P81095E55-E 6-5
Packet Data Flow
The Packet Data network link is dynamic. The actual data rate and flow will depend
on the traffic on the system. As the traffic on the system and the integrity of the
radio link changes the radio link can adapt to the optimum date flow rate. To
optimize performance and resources the iDEN system uses three principles to control
the On-Air interface.
• Dynamic Channel Allocation
• Adaptive Rate Modulation
• Queued Continuous Reservation ALOHA
Dynamic Channel Allocation Procedure
Dynamic Channel Allocation Procedure (DCAP) uses the Broadcast Control
Channel (BCCH) to control the amount of the TDMA timeslots to be used as a
Packet Channel (PCH) for data transmission. In cases of no or low traffic all of the
radio link maybe used to carry data only (1:1 interleaving). If 1:1 interleaving is
used, DCAP uses all the channels and dynamic changes are not allowed. Packet
Data will still require some control and monitoring overhead so not all frames will be
data (the link is not truely peer-to-peer).
Allocation of radio link frame slots places highest priority on voice packets. When
traffic increases the number of slots is altered to reflect the change in traffic. High
voice traffic conditions may pause data transfer (0:1 interleaving) How data packets
are allocated is a provider selected channel sizing option. The options are:
• 1:1 interleave - only transmit packet data (except 1 PCH per cell)
• 3:1 interleave - two data packets per frame minimum
• 6:1 interleave - one data packet per frame minimum
• 12:1 interleave - one data packet every other frame minimum
• 0:1 interleave - transmit no data during high voice traffic
Any number of slots from the maximum to the selected minimum can be used. in
response to the voice traffic.
Adaptive Rate Modulation
The iDEN system continuously monitors the radio link and will alter the method of
modulation of data packets on the RF carrier. As the signal degrades, the amount of
data on the carrier is reduced to improve data recognition and reduce the error rates.
Three modulation methods are used. The methods and the full (1:1 interleaving)
data rates are:
• 64 Quadrature Amplitude Modulation (64-QAM) at 44 kbs with C/N+I
greater than 22dB
• 16 Quadrature Amplitude Modulation (16-QAM) at 22 kbs with C/N+I
greater than 18dB
• Quadrature phase shift keying-compatible (QPSK) at 11 kps with C/N+I
between 18dB toward link failure
The Base Radio must not have a Primary Control Channel allocated and the MS
must be high speed compatible to support the 44 kbs data rate. If a Base Radio
supports the Primary Control Channel, the data rate is limited to 22 kbs.
As the signal degrades the amount of data on the carrier is reduced to improve data
recognition and reduce the error rates.