Agostinho_presentation Chapter three 3.ppt

Telecommunications and Multimedia Unit
UTRA TDD Overview
Agostinho Castro
alcastro@inesporto.pt
Rui Sarmento Castro
rui.castro@inescporto.pt

Outline
• Introduction
– Definition, Principles and Characteristics
• UTRA TDD Physical Channels Structure
– Frame, Slot and Burst
• Mapping of Transport Channels to Physical Channels
• Power Control
• Resource Allocation
– Code Allocation Strategies (FDD)
– Dynamic Channel Allocation (TDD)
• UTRA TDD Interference Scenario

Introduction
• Two implementations are proposed for the UTRA (UMTS
Terrestrial Radio Access) physical layer:
– Frequency Division Duplex (FDD)
– Time Division Duplex (TDD)
Downlink
Uplink
5MHz 5MHz
190MHz
Frequency
Time
5MHz
Downlink
Uplink
Time
Frequency
Guard Period

UTRA FDD
– Requires the allocation of two frequency bands: one for the
uplink and another for the downlink.
– FDD radio units need duplexers in order to separate the
incoming and outgoing signals at the antenna.
– FDD does not allocate efficiently the available bandwidth for
all types of services.

UTRA TDD
– TDD mode can use the same frequency band for both the
uplink and the downlink by allocating distinct time slots to the
two links .
– Each time slot can be allocated either to the uplink or to the
downlink.
– TDD terminals do not need duplexer hence have less
hardware complexity than FDD terminals.
– TDD requires better time synchronization between the users
than FDD
• the base station cannot be allowed to transmit at the
same time as the mobiles stations.
• a guard period must be included in the protocol to make
sure only one link is active at the same time.

UTRA TDD Characterics
• Utilization of unpair band;
• Asymmetric uplink/downlink capacity allocation;
• Discontinuos transmission;
• Interference between uplink and downlink;
• Reciprocal channel.
Downlink
Uplink
Time
Frequency
Guard Period

UTRA TDD
• Combination of TDMA and CDMA
– TD/CDMA
• Direct Sequence CDMA (SS Technique)
Frequency
Time
10 ms
5 MHz
Uplink (MS -> BS)
Downlink (BS -> MS)

UTRA TDD
Frequency
Time
10 ms
5 MHz
Time
Code

UTRA TDD Physical Channel Structure
TDD Frame 10ms (15 timeslots)
MS TX Part
BS TX Part
Spreading
Codes
0,666 ms
Slot
0,666*15=10ms
Burst
DATA
MIDAMBLE
DATA
GUARD PERIOD

UTRA TDD Frame Structure
• Switching point configurations
– Multiple-switching-point (symetric DL/UL allocation)
– Multiple-switching-point (asymetric DL/UL allocation)
– Single-switching-point (symetric DL/UL allocation)
– Single-switching-point (asymetric DL/UL allocation)
10ms
10ms
10ms
10ms

Asymmetrical Capacity Allocation
• Part of the slots must be fixed for
– Downlink: BCH and SCH
– Uplink: RACH
• Other slots could be allocated according to need
(DCA)

Physical Channels
• A Physical Channel in TDD is a BURST
• A BURST is a combination of DATA part, a
MIDAMBLE and a GUARD PERIOD
• Several BURST can be transmitted at the same time
from one transmitter. The DATA part must use
different OVSF channelisation codes (the same
scrambling code)
• The duration of a BURST is one time slot

Bursts Types
• Burst Type 1
– Burst Type 1 can be used for up- and downlink;
• Burst Type 2
– Burst Type 2 can be used for up- and downlink;
• Burst Type 3
– Burst Type 3 is used for uplink only;
Training Sequence
Traffic Burst, PRACH Burst, SCH Burst

Mapping of the Transport
Channels to Physical Channels

Power Control
• Power Control
– Low SF – low processing gain;
– Uplink – Open Loop;
– Downlink – SIR based closed inner loop.

Dynamic Resource Allocation
• FDD
– Code Allocation Strategies
• TDD
– Channel Allocation
– Resource Unit (RU) Allocation - timeslot and code
(frequency)
• Resource Allocation to cells (Slow DCA)
• Resource Allocation to bearer Service (Fast
DCA)

Dynamic Channel Allocation
• Resource Allocation to cells (Slow DCA)
– RNC
• Resource Allocation to bearer Service (Fast DCA)
– Base Station

Dynamic Channel Allocation
(DCA)
Fast
DCA Nk
Fast
DCA N(k+1)
Fast
DCA A1
Fast
DCA A2
Slow DCA A Slow DCA N
RNC
BS A1
BS A2
BS Nk
BS N(k+1)

TDD Interference Scenario
BS 1 BS 2
MS 1 MS 2
T T T T R R R R R R R R R R
R T T T T T T T T T
R R T
R
BS 1
MS 1
R R R R R R R T T T T T T T
R R
T T T T T T T T R R R
R
MS 2
BS 2
High power
BS1 blocks MS2 in BS2

Packet Access
• A packet service session contains one or several
PACKET CALLS depending on application;
• PACKET CALLS constitues a BURSTY SEQUENCE
OF PACKETS;

Packet Data Traffic
• Characteristics
– Session arrival process;
– Number of packet calls per session;
– Reading time between packets calls;
• Reading time starts when the last packet of the
packet call is completely received by the user
and ends when user makes a request for the
next packet call.
– Time interval between two packets inside a packet
call;
– Packet size.

Packet Data Traffic

Non-real Time Packet Service
• Characteristics from air interface point of view
– Packet data is BURSTY;
– Packet data tolerates longer delay then real-time
services;
– Packets can be retransmited by Radio Link
Control (RLC).

WCDMA Packet Access
• Packet allocations in WCDMA are controlled by the
PACKET SCHEDULER (PS)
• Packet Scheduler Functions
– Divide the avaiable air interface

Packet Data Service
• Model of Operation in WCDMA (uplink)
– Packet data can be transmited in three ways
• Packet transmission on the RACH;
• Packet transmission on a dedicated channel;
• Packet transmission on a dedicated channel
(when there is already a dedicated channel
available).

Packet Transmission on the RACH
• Packet is included in the message part of the access
burst;
• If there is a small amount of data to transmit;
– Short message service;
– Short text-only e-mails.
• No explicit reservation is carried out;
• No explicit channel assignment is needed;
• Risk of collisions on the common RACH;
• Not power-controlled.

Packet Transmission on Dedicated Channels
• MS first sends a resource request message,
indicating what type of traffic is to be transmitted;
• Network evaluates whether the MS can be assigned
the necessary resource;
– YES
• A resource allocation message (RAM) is
transmitted on the FACH.
• RAM consists of a set of transport formats and the
specification of a dedicated channel to use for the
packet transmission,
• (out of this set) MS will use one transport format to
transmit the data on a DCH;

Packet Transmission on Dedicated Channels
(cont.)
• EXACTLY which transport format the MS may use
and at what time the MS may initiate its transmission
is EITHER transmitted TOGETHER with RAM (traffic
load is low) OR is indicated in a separate capacity-
allocation message AT LATER TIME;
• The second alternative is used in cases where the
load is high AND the MS is not allowed to
immediately transmit the the packet;

Packet transmission on a dedicated channel (when there is already
a dedicated channel available).
• It is used when there is already a dedicated channel
available;
• MS can then either issue a capacity request on the
DCH, when the MS has a large amount of data to
transmit OR simply start

Agostinho_presentation Chapter three 3.ppt

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