2. Cordless System Operating Environments
Residential – a single base station can
provide in-house voice and data support
Office
A single base station can support a small office
Multiple base stations in a cellular
configuration can support a larger office
Telepoint – a base station set up in a public
place, such as an airport
3. Design Considerations for Cordless Standards
Modest range of handset from base station,
so low-power designs are used
Inexpensive handset and base station,
dictating simple technical approaches
Frequency flexibility is limited, so the
system needs to be able to seek a low-
interference channel whenever used
4. Time Division Duplex (TDD)
TDD also known as time-compression
multiplexing (TCM)
Data transmitted in one direction at a time,
with transmission between the two
directions
Simple TDD
TDMA TDD
5. Simple TDD
Bit stream is divided into equal segments,
compressed in time to a higher transmission rate,
and transmitted in bursts
Effective bits transmitted per second:
R = B/2(Tp+Tb+Tg)
R = effective data rate
B = size of block in bits
Tp = propagation delay
Tb = burst transmission time
Tg = guard time
6. Simple TDD
Actual data rate, A:
A = B /Tb
Combined with previous equation:
The actual data rate is more than double the
effective data rate seen by the two sides
+
+=
b
gp
T
TT
RA 12
7. TDMA TDD
Wireless TDD typically used with TDMA
A number of users receive forward channel
signals in turn and then transmit reverse
channel signals in turn, all on same carrier
frequency
Advantages of TDMA/TDD:
Improved ability to cope with fast fading
Improved capacity allocation
8. DECT Frame Format
Preamble (16 bits) – alert receiver
Sync (16 bits) – enable receiver to
synchronize on beginning of time slot
A field (64 bits) – used for network control
B field (320 bits) – contains user data
X field (4 bits) – parity check bits
Guard (60 bits) – guard time, Tg
9. A Field Logical Control Channels
Q channel – used to broadcast general system
information from base station to all terminals
P channel – provides paging from the base station
to terminals
M channel – used by terminal to exchange
medium access control messages with base station
N channel – provides handshaking protocol
C channel – provides call management for active
connections
10. B Field
B field transmits data in two modes
Unprotected mode - used to transmit digitized
voice
Protected mode - transmits nonvoice data traffic
12. DECT Protocol Architecture
Physical layer – data transmitted in TDMA-TDD
frames over one of 10 RF carriers
Medium access control (MAC) layer – selects/
establishes/releases connections on physical
channels; supports three services:
Broadcast
Connection oriented
Connectionless
Data link control layer – provides for the reliable
transmission of messages using traditional data
link control procedures
