Литература / UMTS-Report

ETSI SMG2#24 TDoc SMG2 368 / 97

Cork, Ireland

December 1-5, 1997

Concept Group Delta

Wideband TDMA/CDMA

Evaluation Report - Part 1

V 2.0 b

1 Introduction

In the procedure to define the UMTS Terrestrial Radio Access (UTRA), the wideband TDMA/CDMA concept group develops and evaluates a multiple access concept based on time, frequency and code division. This group basically includes the FRAMES Multiple Access Mode 1 (FMA1) with spreading proposal.

Intention of this document is to present detailed technical data and evaluation results for the concept discussed in this group.

The final version 2.0 b of the evaluation report contains 6 parts:

Part 1: Description of the proposal

Part 2: Mixed services in Wideband TDMA/CDMA

Part 3: Link level simulation results

Part 4: System level simulation results

Part 5: Template according UMTS 30.03, annex 1

Part 6: Support for Relaying and ODMA

1.1Contact Persons

3 Logical channels

This chapter describes the logical channels required for data transfer. Logical channels are unidirectional and can be divided into two categories:

∙Traffic channels and

∙Control channels

3.1Traffic channels

A traffic channel (TCH) is used for transferring user data and / or layer 3 signalling data.

3.2Control channels

Control channels carry layer 3 and MAC signalling data and they are also needed for the initial synchronization of the mobile station. Control channels can be further divided into:

∙Dedicated control channels and

∙Common control channels.

3.2.1Dedicated Control Channels

Dedicated Control Channels (DCCH) are point-to-point control channels that carry connection oriented messages.

1.Associated Control Channel (ACCH) is a point-to-point channel in the uplink or downlink direction. The allocation of an ACCH is linked to the allocation of a TCH. The ACCH is used for RLC/MAC layer messages, e.g. capacity allocations or link control messages.

2.Stand-alone DCCH (SDCCH) is a point-to-point channel in the uplink or downlink direction. The allocation of an SDCCH is not linked to the allocation of a TCH, MAC may or may not allocate SDCCH capacity to an MS dependent upon circumstances. An SDCCH is used for the transfer of layer 3 and RLC/MAC layer messages.

3.2.2Common Control Channels

Common Control Channels (CCCH) are point-to-multipoint or point-to-point control channels that carry connectionless or connection oriented messages.

The Pilot Channel PICH is transmitted at a constant power by the BS on the BCCH carrier. In FDD mode, it is transmitted continuously (on all time slots per frame). In TDD mode, it is transmitted only during the downlink time slots. The PICH is used by the mobile stations to perform power measurements (for cell (re-)selection and mobile assisted handover) and to acquire initial frequency and time slot synchronization (time slot boundary).

The Pilot Channel is based on a long chip-sequence hidden under the data channels by large spreading; the transmitted power of the PICH is expected to be 16 dB below the highest allowed power of any downlink data channel. The long chip sequence used for synchronization matches the time-slot length of 1250 chips. Eight orthogonal sequences are defined. They are allocated on a base station basis to control the risk of interference between close cells sharing the same frequency.

At power up or during the monitoring of adjacent cells, the mobile station scans for one of the eight possible sequences over windows of 2 x 1250 chips to determine the time and frequency synchronization. The result of the autocorrelation is a good estimate of the received power level. It must be pointed out that the eight sequences can be simultaneously analysed, which may allow the mobile station, from the same set of samples, to get power measurements and synchronization from several base stations sharing the same BCCH frequency.

The Broadcast Control Channel BCCH is mapped onto a predefined time-slot (e.g. time-slot 0) and predefined spreading code, hereafter called BCCH spreading code. The BCCH logical channel may occupy partly or fully the corresponding resource unit, apart from the 13th frames carrying SCH, dedicated signaling or idle frames, as explained later. This is illustrated in the figure below. Additional resource units located anywhere in terms of slot or frequency may carry additional BCCHs. The exact position of these additional channels is indicated in the “primary” BCCH (e.g. on TS 0).

one superframe

multiframe

Mapping of the BCCH logical channel

The Paging Channel PCH can be mapped on any combination of time slots and codes on the BCCH carrier, and it can occupy partly or fully the correspondingresource units, apart from the 13th frames carrying SCH or dedicated signalling. In case other frequencies carry additional BCCH, they can also carry additional PCH. The exact location of the PCH is indicated on the BCCH. Of course, the chosen location must allow efficient DRX. One possibility is to map PCH on TS 0 of the BCCH carrier and on the BCCH spreading code (BCCH and PCH thus sharing the sameresource unit).

The Random Access Channel RACH (both N-RACH and S-RACH) has an interleaving period of one frame and each transmission occupies only one burst.

The N-RACH is an uplink contention access signalling channel for MS being time-aligned that is used to transfer MAC related signalling to the network (e.g. capacity requests). It can be mapped on anyresource unit and it can occupy it partly or fully, apart from the 13th frames. Its location can be

indicated on the BCCH or on the FACH. The total N-RACH capacity may be subdivided amongst a number of access groups.

The S-RACH is used by a mobile station that needs to access the network without knowing its timing advance (either on initial access or for handover access in the case of asynchronous handovers). Characteristics of the joint detection impose that S-RACH bursts are not transmitted simultaneously to traffic bursts. A fixed (basic) mapping on the multiframe structure can be used, whereby the S-RACH are mapped on some of the 13th frames on each time slot and on each carrier; as an example, the S- RACH can be mapped on 5 multiframes out of the 9 multiframes of a superframe, as shown in the next figure. This mapping applies both to FDD and TDD modes, but, in TDD, only the uplink time slots can be used.

Of course, other dynamic or extended mappings are possible; for example, in order to increase the S- RACH capacity, time slots of the 12 first frames of the multiframe may be partly or fully allocated in the uplink for random access opportunities.

one superframe

multiframe

Mapping of the basic S-RACH on all time-slots and all carriers for the fixed mapping case

Since transmitting random accesses and monitoring neighbouring cells can be considered as two mutually exclusive actions, the 13th uplink frames reserved for S-RACH in the fixed mapping case are also the “idle” frames. The corresponding downlink frames are also idle.

The Forward Access Channel FACH can be mapped on any combination/fraction of downlinkresource units. Again, the 13th frames cannot be used for the FACH. The FACH can be segmented into a number of parallel channels each serving a group of MS if required.

The Uplink Assigned Channel UACH can be allocated anyresource unit on the uplink (not on the 13th frames), but the allocation is made for the transfer of only one message (e.g. acknowledgement or forward order message).