UTRA TDD Overview

1
UTRA TDD Overview

• Agostinho Castro
• alcastro_at_inesporto.pt
• Rui Sarmento Castro
• rui.castro_at_inescporto.pt

2
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

3
Introduction

• Two implementations are proposed for the UTRA
  (UMTS Terrestrial Radio Access) physical layer
• Frequency Division Duplex (FDD)
• Time Division Duplex (TDD)

5MHz
4
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.

5
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.

6
UTRA TDD Characterics

• Utilization of unpair band
• Asymmetric uplink/downlink capacity allocation
• Discontinuos transmission
• Interference between uplink and downlink
• Reciprocal channel.

7
UTRA TDD

• Combination of TDMA and CDMA
• TD/CDMA
• Direct Sequence CDMA (SS Technique)

Time
Frequency
10 ms
5 MHz
8
UTRA TDD
Time
Frequency
10 ms
5 MHz
9
UTRA TDD Physical Channel Structure
TDD Frame 10ms (15 timeslots)
MS TX Part
BS TX Part
0,6661510ms
10
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)

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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)

12
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

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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
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Mapping of the Transport Channels to Physical
Channels
15
Power Control

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

16
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)

17
Dynamic Channel Allocation

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

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Dynamic Channel Allocation (DCA)
BS Nk
RNC
Slow DCA A
Slow DCA N
BS N(k1)
BS A1
BS A2
19
TDD Interference Scenario
High power
BS1 blocks MS2 in BS2
BS 1
MS 1
MS 2
BS 1
BS 2
BS 2
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Packet Access

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

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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.

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Packet Data Traffic
23
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).

24
WCDMA Packet Access

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

25
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).

26
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.

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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

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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

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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