5.8 Idle periods for IPDL location method

25.2243GPPPhysical layer procedures (TDD)TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

5.8.1 General

To support time difference measurements for location services, idle periods can be created in the downlink (hence the name IPDL) during which time transmission of the DwPCH from a Node B is temporarily ceased. During these idle periods the visibility of neighbour cells from the UE is improved.

The idle periods are arranged in a determined pattern according to higher layer parameters. An idle period has a duration of one DwPTS.

In general there are two modes for these idle periods:

– Continuous mode, and

– Burst mode

In continuous mode, the idle periods are active all the time. In burst mode the idle periods are arranged in bursts where each burst contains enough idle periods to allow a UE to make sufficient measurements for its location to be calculated. The bursts are separated by a period where no idle periods occur. The time difference measurements can be performed on any channel.

5.8.2 Parameters of IPDL

The following parameters are signalled to the UE via higher layers:

IP_Status: This is a logic value that indicates if the idle periods are arranged in continuous or burst mode.

IP_Spacing: The number of 10 ms radio frames between the start of a radio frame that contains an idle period and the next radio frame that contains the next idle period.

IP_Start: The number of the first frame with idle periods. In case of continuous mode IP_Start is the SFN of the first frame with idle periods and in case of burst mode IP_Start defines the number of frames after Burst_Start with the first frame with idle periods.

IP_Sub: Indicates whether the idle period is to occur in the odd, the even or both the odd and even 5 ms sub-frames of the 10 ms idle frame.

Additionally in the case of burst mode operation the following parameters are also communicated to the UE.

Burst_Start: Specifies the start of the first burst of idle periods. 256Burst_Start is the SFN where the first burst of idle periods starts.

Burst_Length: The number of idle periods in a burst of idle periods.

Burst_Freq: Specifies the time between the start of a burst and the start of the next burst. 256Burst_Freq is the number of radio frames between the start of a burst and the start of the next burst.

5.8.3 Calculation of idle period position

In burst mode, burst #0 starts in the radio frame with SFN = 256Burst_Start. Burst #n starts in the radio frame with SFN = 256Burst_Start + n256Burst_Freq ( n = 0,1,2, …). The sequence of bursts according to this formula continues up to and including the radio frame with SFN = 4095. At the start of the radio frame with SFN = 0, the burst sequence is terminated (no idle periods are generated) and at SFN = 256Burst_Start the burst sequence is restarted with burst #0 followed by burst #1 etc., as described above.

Continuous mode is equivalent to burst mode, with only one burst spanning the whole SFN cycle of 4096 radio frames, this burst starts in the radio frame with SFN = 0. In case of continuous mode the parameter IP_Start defines the first frame with idle periods.

The DwPCH, that has to be idle, is defined by two values: IP_Frame(x) and IP_Sub. IP_Frame(x) defines the x^th frame within a burst in which subframe with the number IP_Sub has to be switched off.

The actual frame with idle periods within a burst is calculated as follows:

IP_Frame(x) = IP_Start + (x-1)  IP_Spacing with x = 1, 2, 3, ….

Figure 11 below illustrates the idle periods for the burst mode which shows the case that both subframes within each frame have DwPTS as an idle period.

Figure 11: Idle periods of burst mode for 1.28Mcps TDD