iDEN (Integrated Dispatch Enhanced Network)

iDEN (Integrated Dispatch
Enhanced Network)
The iDEN system is a unique wireless access platform because it involves
integrating several mobile phone technologies together, which is based on a modified GSM platform. The services that are integrated into iDEN involve
a dispatch system, full-duplex telephone interconnections, data transport,
and short messaging services.
The dispatch system involves a feature called group call, where multiple
people can engage in a conference. The user list is preprogrammed and the
conference call can be set up just like it is done in two-way or specialized
mobile radio (SMR) with the exception that the connection can take place
utilizing any of the frequencies that are available from the pool of channels
where the subscriber is physically located.
The telephone interconnect and data transport are meant to offer conventional
mobile communications. The short messaging service enables the
iDEN phones to receive up to 140 characters for an alphanumeric message.
An example of a typical iDEN system is shown in Figure 3-33.
The elements that comprise the iDEN system, as shown in Figure 3-33,
are briefly listed here:
DAP—Dispatch Application Processor
EBTS—Enhanced Base Transceiver

HLR—Home Location Register
MPS—Metro Packet Switch
MSC—Mobile Switching Center
OMC—Operations and Maintenance Center
SMS-SC—Short Message Service-Service Center
XCDR—Transcoder
In review of Figure 3-33, there are several differences with an iDEN system
as compared to a typical mobile wireless system. iDEN is unique in wireless
mobility because it combines both interconnect as well as dispatch
services in the same wireless system. The two distinct systems, interconnect
and dispatch, are effectively overlaid on top of each other but are integrated
and share some common elements like the EBTS radio.
The BSC is responsible for traffic and control channel allocations in addition
to handover data collection and controlling handovers between other
BSCs.

The Metro Packet Switch (MPS) provides the connectivity for the dispatch
calls. It also distributes the dispatch packets as well as the ISMI
assignment.
The Dispatch Application Processor (DAP) is the processing entity
responsible for overall coordination and control of the dispatch services.The
DAP enables the following types of calls to take place:
■ Talk group
■ Private call
■ Call alert
The radio access system used by an iDEN system is TDMA.The channel
bandwidth is 25 kHz, which consists of four independent side bands, each
being a 16QAM baseband signal. The center frequencies of these side bands
are 4.5 kHz apart from each other, and they are spaced symmetrically about
a suppressed RF carrier frequency, resulting in a 16-point data symbol constellation
that carries four data bits per symbol. The location where iDEN
is utilized in the spectrum is shown in Figure 3-34. The RF channel structure
is shown in Figure 3-35.
iDEN was introduced using a 6:1 interleave for both dispatch and interconnect
services. Later the system was upgraded, enabling a 3:1 interleave
for interconnect-only service.
The wireless operator has the choice of offering 6:1 or 3:1 voice service in
addition to dispatch. Capacity is affected by the selection of which interconnection
method is used and the amount of dispatch traffic that is carried
on a system. Looking at a simplistic example, the 3:1 voice call requires two
TCHs, while a 6:1 or dispatch call requires only a single TCH. Of course,
other issues related to signaling and call quality are factored into this.
iDEN utilizes several control channels similar in nature to GSM systems.
The control channels used by iDEN systems are listed here for reference.
In addition to the control channels, two other channels are used in
iDEN; they are the TCH and PCH, also listed.
■ PCCH The primary control channel is a multiple access channel
used for the transmission of general system parameters. The outbound
PCCH contains the broadcast control channel (BCCH) and the
common control channel (CCCH), whereas the inbound PCCH is
referred to as the random access channel (RCCH):
■ Inbound Service requests
■ Outbound Service grants
■ BCCH

■ Neighbor cells
■ Control channels
■ Packet channels
■ Location areas
■ Common control channel
■ Paging subchannel
■ Service grants
■ TCCH Temporary control channel
■ Inbound Dispatch reassignment requests
■ Outbound Handover target
■ DCCH Dedicated control channel
■ Inbound Location updating
■ Authentication
■ SMS
■ Registration
■ Outbound
■ Location updating
■ Authentication
■ SMS
■ Registration
■ ACCH Associated control channel
■ TCH Traffic channel that provides circuit mode transmission for
voice and data
■ Inbound Dispatch reassignment requests
■ Outbound Handover target
■ PCH Packet channel provides for multi-access packet mode
transmission

Many interesting issues are associated with the iDEN call processing for
either dispatch or interconnection calls. From the time an iDEN mobile
subscriber is initially powered up until it is powered down, a series of procedures
are executed between the EBTS and the MOBILE to control the
radio communications link. Before a call description flow chart is shown, a
few terms or processes used in iDEN systems associated with the mobile
need to be briefly covered.