4 The physical resource

05.023GPPMultiplexing and Multiple Access on the Radio PathTS

4.1 General

The physical resource available to the radio sub‑system is an allocation of part of the radio spectrum. This resource is partitioned both in frequency and time. Frequency is partitioned by radio frequency channels (RFCHs) divided into bands as defined in GSM 05.05. Time is partitioned by timeslots, TDMA frames, and (for COMPACT) time groups and 52-multiframe number as defined in clause 4.3 of the present document.

4.2 Radio frequency channels

4.2.1 Cell allocation and mobile allocation

GSM 05.05 defines radio frequency channels (RFCHs), and allocates numbers to all the radio frequency channels available to the system. Each cell is allocated a subset of these channels, defined as the cell allocation (CA). One radio frequency channel of the cell allocation shall be used to carry synchronization information and the BCCH, this shall be known as BCCH carrier. The subset of the cell allocation, allocated to a particular mobile, shall be known as the mobile allocation (MA).

For COMPACT, one radio frequency channel of the cell allocation shall be used to carry synchronization information and the CPBCCH, this shall be known as the primary COMPACT carrier. All other radio frequency channels of the cell allocation shall be known as secondary COMPACT carriers.

4.2.2 Downlink and uplink

The downlink comprises radio frequency channels used in the base transceiver station to Mobile Station direction.

The uplink comprises radio frequency channels used in the mobile station to base transceiver station direction.

4.3 Timeslots, TDMA frames, and time groups

4.3.1 General

A timeslot shall have a duration of 3/5 200 seconds ( 577 µs). Eight timeslots shall form a TDMA frame ( 4,62 ms in duration).

At the base transceiver station the TDMA frames on all of the radio frequency channels in the downlink shall be aligned. The same shall apply to the uplink (see GSM 05.10).

At the base transceiver station the start of a TDMA frame on the uplink is delayed by the fixed period of 3 timeslots from the start of the TDMA frame on the downlink (see figure 2).

At the mobile station this delay will be variable to allow adjustment for signal propagation delay. The process of adjusting this advance is known as adaptive frame alignment and is detailed in GSM 05.10.

The staggering of TDMA frames used in the downlink and uplink is in order to allow the same timeslot number to be used in the downlink and uplink whilst avoiding the requirement for the mobile station to transmit and receive simultaneously. The period includes time for adaptive frame alignment, transceiver tuning and receive/transmit switching (see figure 4).

4.3.2 Timeslot number

The timeslots within a TDMA frame shall be numbered from 0 to 7 and a particular timeslot shall be referred to by its timeslot number (TN).

4.3.3 TDMA frame number

TDMA frames shall be numbered by a frame number (FN). The frame number shall be cyclic and shall have a range of 0 to FN_MAX where FN_MAX = (26 x 51 x 2048) ‑1 = 2715647 as defined in GSM 05.10. For COMPACT, FN_MAX = (52 x 51 x 1024) -1 = 2715647. The frame number shall be incremented at the end of each TDMA frame.

The complete cycle of TDMA frame numbers from 0 to FN_MAX is defined as a hyperframe. A hyperframe consists of 2048 superframes where a superframe is defined as 26 x 51 TDMA frames. For COMPACT, a hyperframe consists of 1024 superframes where a superframe is defined as 52 x 51 TDMA frames. A 26‑multiframe, comprising 26 TDMA frames, is used to support traffic and associated control channels and a 51- multiframe, comprising 51 TDMA frames, is used to support broadcast, common control and stand alone dedicated control (and their associated control) channels. Hence a superframe may be considered as 51 traffic/associated control multiframes or 26 broadcast/common control multiframes. A 52‑multiframe, comprising two 26‑multiframes, is used to support packet data traffic and control channels.

The need for a hyperframe of a substantially longer period than a superframe arises from the requirements of the encryption process which uses FN as an input parameter.

Time group

Used for COMPACT, time groups shall be numbered from 0 to 3 and a particular time group shall be referred to by its time group number (TG) (see clause 3.3.2.2.2). At block B0 and frame number (FN) mod 208 = 0, time group numbers (TG) are associated with timeslot numbers (TN) as follows:

TG

TN

0

1

1

3

2

5

3

7

For COMPACT, a cell is assigned one time group number (TG) on a primary COMPACT carrier. This is known as the serving time group. Other cells may be assigned other time groups on the same carrier.