Telecommunications and Multimedia Unit UTRA TDD Overview Agostinho Castro Rui Sarmento Castro

Telecommunications and Multimedia Unit 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

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

Telecommunications and Multimedia Unit 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.

Telecommunications and Multimedia Unit 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.

Telecommunications and Multimedia Unit 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

Telecommunications and Multimedia Unit 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)

Telecommunications and Multimedia Unit UTRA TDD Frequency Time 10 ms 5 MHz Time Code

Telecommunications and Multimedia Unit UTRA TDD Physical Channel Structure TDD Frame 10ms (15 timeslots) MS TX PartBS TX Part Spreading Codes 0,666 ms Slot 0,666*15=10ms Burst DATAMIDAMBLEDATA GUARD PERIOD

Telecommunications and Multimedia Unit 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

Telecommunications and Multimedia Unit 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)

Telecommunications and Multimedia Unit 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

Telecommunications and Multimedia Unit 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

Telecommunications and Multimedia Unit Mapping of the Transport Channels to Physical Channels

Telecommunications and Multimedia Unit Power Control –Low SF – low processing gain; –Uplink – Open Loop; –Downlink – SIR based closed inner loop.

Telecommunications and Multimedia Unit 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)

Telecommunications and Multimedia Unit Dynamic Channel Allocation Resource Allocation to cells (Slow DCA) –RNC Resource Allocation to bearer Service (Fast DCA) –Base Station

Telecommunications and Multimedia Unit 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)

Telecommunications and Multimedia Unit TDD Interference Scenario BS 1 BS 2 MS 1MS 2 TTTTRRRRRRRRRR RTTTTTTTTTRRTR BS 1 MS 1 RRRRRRRTTTTTTT RRTTTTTTTTRRRR MS 2 BS 2 High power BS1 blocks MS2 in BS2

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

Telecommunications and Multimedia Unit 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.

Telecommunications and Multimedia Unit Packet Data Traffic

Telecommunications and Multimedia Unit 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).

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

Telecommunications and Multimedia Unit 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).

Telecommunications and Multimedia Unit 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 s. No explicit reservation is carried out; No explicit channel assignment is needed; Risk of collisions on the common RACH; Not power-controlled.

Telecommunications and Multimedia Unit 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;

Telecommunications and Multimedia Unit 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;

Telecommunications and Multimedia Unit 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