H.1 TOA LMU Requirements

05.053GPPRadio transmission and receptionTS

A TOA Location Measurement Unit (LMU) is a unit for making accurate Time-of-Arrival (TOA) measurements. Specifically, the LMU shall be capable of measuring the Time-of-Arrival of access bursts that are transmitted from a mobile station on request. The measurement results are used by the system for determining the location of the mobile station as described in 3GPP TS 03.71. This section defines the requirements for the receiver of an LMU deployed in the GSM system. Requirements are defined for the Time-of-Arrival measurement accuracy of the LMU.

In addition, an LMU shall be capable of performing Radio Interface Timing (RIT) measurements, comprising Absolute Time Differences (ATD), as described in 3GPP TS 03.71.

H.1.1 Void

H.1.2 LMU characteristics

In this clause, the requirements are given in terms of power levels at the antenna connector of an LMU. Equipment with an integral antenna may be taken into account in a similar manner as described in Chapter 5 of 3GPP TS 05.05.

H.1.2.1 Blocking characteristics

This subclause defines receiver blocking requirements. The reference sensitivity performance as specified in Table H.1.2 shall be met when the following signals are simultaneously input to the LMU.

– A carrier signal as described in H.1.3.1 at frequency f0, 9 dB above the reference sensitivity level as specified in Table H.1.1.

– A continuous static sine wave signal as described in Section 5.1 of 3GPP TS 05.05. The requirements for normal “BTS” shall be used, however the signal strength shall be 6 dB higher than the requirements for “normal BTS”.

The exceptions listed in Section 5.1 of 3GPP TS 05.05 apply also for the LMU requirements.

H.1.2.2 AM suppression characteristics

This subclause defines AM suppression requirements. The reference sensitivity performance as specified in Table H.1.2 shall be met when the following signals are simultaneously input to the LMU.

– A carrier signal as described in H.1.3.1 at frequency f0, 9 dB above the reference sensitivity level as specified in Table H.1.1.

– A single frequency signal as described in Section 5.2 of 3GPP TS 05.05. The requirements for “normal BTS” shall be used, however the signal strength shall be 6 dB higher than the requirements for “normal BTS”.

H.1.2.3 Intermodulation characteristics

This subclause defines intermodulation requirements. The reference sensitivity performance as specified in Table H.1.2 shall be met when the following signals are simultaneously input to the LMU.

– A carrier signal as described in H.1.3.1 at frequency f0, 9 dB above the reference sensitivity level as specified in Table H.1.1.

– A continuous static sine wave signal and any 148-bit subsequence of the 511-bits pseudo-random sequence in CCITT O.153. The signal strength shall be 6 dB higher than as described in Section 5.3 of 3GPP TS 05.05.

H.1.2.4 Spurious emissions

The requirements for a BTS receiver as specified in section 5.4 of 3GPP TS 05.05 shall apply also to the receiver of an LMU.

H.1.3 Time-of-Arrival Measurement Performance

This clause specifies the required Time-of-Arrival (TOA) measurement accuracy of the LMU with and without interference and different channel conditions. The requirements are given in terms of Time-of-Arrival measurement error (in microseconds) as a function of the carrier and interference input power levels at the antenna connector of the receiver. Equipment with an integral antenna may be taken into account in a similar manner as described in Chapter 5 of 3GPP TS 05.05.

The power level, under multipath fading conditions, is the mean power of the sum of the individual paths.

H.1.3.1 Sensitivity Performance

With the following configuration and propagation conditions, the LMU shall meet the requirements for 90% RMS TOA error (RMS90) defined in Table H.1.2.

– A carrier signal of GMSK modulated random access bursts is fed into the LMU. The duration of the carrier signal is 320 ms. The access bursts occur once every TDMA frame in a 26-frame multiframe, except in frame number 12 and 25.

NOTE: Since it is an implementation option in the MS whether or not a MS transmits access bursts during SACCH frames (i.e. frame number 12 or 25 in a 26-frame multiframe), this test carrier signal specifies the worst case under which the requirements shall be met.

– The access bursts consist of a fixed training sequence according to 3GPP TS 05.02 and a data part. The data part of the access burst is random but constant over one 320 ms measurement trial. The data part of the access burst is made known to the LMU before a measurement starts.

– The power up and power down ramping for the bursts is in accordance with Annex B of 3GPP TS 05.05.

– The measurement accuracy of the LMU is defined as the root-mean-square (RMS) value of the most accurate 90% of TOA measurements. As an example, if {x1..xN}is a set of the absolute square Time-of-Arrival measurement errors for N trials, sorted in ascending order, the RMS of 90% is defined as

RMS90 = sqrt( sum(x1..xM)/M ) where M is the largest integer such that M < 0.9 N.

For the test, N > 500 trials is recommended.

– Measurements shall be performed at two signal strength levels for each of two different propagation conditions. The signal strength level requirement in Table G.2 is expressed relative to the reference sensitivity level defined in Table H.1.1.

– For each signal strength, the two channel conditions are:

1) Static

2) Rayleigh (the signal fades with a Rayleigh amplitude distribution and perfect decorrelation between the bursts).

Note: Perfect decorrelation between bursts may be attained using a 100 km/hr mobile velocity for the Rayleigh faded channel.

– The LMU is informed of the true Time-of-Arrival value – with an uncertainty of 20 bit periods (approx. 70ms ) – prior to the measurement. This defines a search window of +/-10 bit periods during which the true Time-of-Arrival will occur (per 3GPP TS 04.71 Annex B, paragraph 3.5). The true Time-of-Arrival value shall be uniformly distributed within the search window for each measurement trial. The TOA measurement error is then defined as the difference between this true Time-of-Arrival value minus the measured TOA value at the LMU.

Table H.1.1: Reference Sensitivity Level

Signal strength at antenna connector

GSM 400, GSM 850, GSM 900, DCS 1800, PCS 1900

-123 dBm

Table H.1.2: Sensitivity performance
(RMS90 of Time-of-Arrival error in microseconds)

Carrier signal strength relative to reference sensitivity level

Static

Rayleigh

0 dB

0.37

0.37

20 dB

0.18

0.18

H.1.3.2 Interference Performance

In this subclause, requirements are given in terms of the TOA measurement accuracy (in microseconds) for a specified carrier to interference ratio (C/I) at the antenna connector of the receiver. The input carrier signal shall be as defined in subclause H.1.3.1 and shall be set to a level 40 dB above the reference sensitivity level defined in Table H.1.1. The C/I requirements shall be met for an interference signal which is co-channel, adjacent channel (200 kHz offset), and alternate channel (400 kHz offset) to the desired signal as specified in table H.1.3.

The interference signal properties and propagation conditions are defined below.

– One interfering signal is present which consists of a sequence of GMSK modulated normal bursts. The training sequence is chosen randomly from the 8 possible normal burst TSC’s defined in 3GPP TS 05.02, but kept fixed during one 320 ms measurement trial.

– The time offset between the carrier and the interferer signal is uniformly distributed random between 0 and 156.25 bit periods, but fixed during one 320 ms measurement trial. The length of the carrier burst (access burst) is 88 bit periods, the length of one burst period is 156.25 bit periods, and the length of the interferer training sequence is 26 bit periods. The probability that the interference training sequence overlaps with some part of the carrier burst is therefore (88+26)/156.25 = 73%.

– Each interference condition shall meet the C/I requirements in Table H.1.3 for the following channel conditions:

1) Static

2) Rayleigh (the signal and interference fade independently with a Rayleigh amplitude distribution that has perfect decorrelation between bursts).

NOTE 1: Perfect decorrelation between bursts may be attained using a 100 km/hr mobile velocity for the Rayleigh faded channel.

– A search window of 20 bit periods shall be used as defined in section H.1.3.1.

NOTE 2: In the case of frequency hopping, the interference and carrier signal shall have the same frequency hopping sequence.

Table H.1.3: Interference performance
(RMS90 of Time-of-Arrival error in microseconds)

90% RMS TOA Error

Interference type

Static

Rayleigh

Carrier to Interference Level (dB)

Co-channel

0,37

0,37

-9 dB

0,18

0,18

5 dB

Adjacent channel
(200 kHz)

0,37

0,37

-20 dB

0,18

0,18

-10 dB

Adjacent channel
(400 kHz)

0,37

0,37

-50 dB

0,18

0,18

-40 dB

H.1.3.3 Multipath Performance

This subclause defines TOA estimation accuracy under multipath conditions. The test setup is per H.1.3.1 (sensitivity performance) with the following changes:

– Each burst propagates through the TU multipath channel specified in Annex C of 3GPP TS 05.05. The true Time-of-Arrival value is the time of the first tap (tap number 1).

– Ideal FH is assumed, i.e. perfect decorrelation between bursts.

NOTE: Perfect decorrelation between bursts may be approximated by using frequency hopping or a 100 km/hr mobile velocity with the TU channel model.

The performance requirements are specified in table H.1.4.

Table H.1.4: Multipath performance
(RMS90 of Time-of-Arrival error in microseconds)

Carrier signal strength relative to reference (Table G.1)

TU3/100
(12 tap setting)

0 dB

0,5

20 dB

0,4

H.1.4 Radio Interface Timing Measurement Performance

A Location Measurement Unit shall be capable of performing Radio Interface Timing (RIT) measurements as described in 3GPP TS 03.71 to support one or more positioning methods. RIT measurements comprise measurements of the synchronization difference between two base transceiver stations. An LMU shall therefore be capable of monitoring multiple base transceiver stations. The measurements of BTS synchronization differences can either be performed relative to a reference BTS (i.e. RTD measurement) or relative to some absolute time scale (i.e. ATD measurement).

The RIT measurement shall be made with an accuracy of 2 bit periods.