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«ETSI TR 101 987 V1.1.1 (2001-08) Technical Report Terrestial Trunked Radio (TETRA); Proposed Air Interface Enhancements for TETRA Release 2; Analysis and ...»

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Frequency Hopping is a major study area that might bring significant benefits to TETRA, but needs to be studied in substantial detail before a decision can be made. This area may require to be sourced from STF support.

6.1.2 Sub-area 2

The terminals sub-area determined that the most feasible options are:

1) Implement the energy economy mode of MS operation (clause 5.3.1) with guidelines on interaction with MM and neighbour cell measurement in the standard. Note this may interact with other clauses that also have some say in the RSS measurement (handover, open loop power control and MS location).

2) Implement discontinuous transmission (clause 5.3.2) with guidelines on the use of hangover times and Voice Activity Detection algorithms. The investigation into a VAD may be a substantial piece of work, or it may be the reuse of existing algorithms. Note the introduction of DTX will reduce uplink interference in duplex calls.

3) Implement the closed loop power control. Note the reduction of MS uplink power will reduce uplink interference.

4) Standardize the RSS measurement methodology. Note this will have an interaction with improved handover and MS location.

5) Change the step size in open loop power control. Note this option may be difficult in the MS hardware.

6) Change the step size in closed loop power control. Note this option may be difficult in the MS hardware.

7) Introduce a new low power class for the MS.

8) Introduce a reduced lower limit to the dynamic range of the power control algorithm.

9) Use the AACH and a reserved "usage marker" to give fast power control feedback.

6.1.3 Sub-area 3 No options discussed at TG23 meetings - see clause 7.3 for details on unstudied options.

–  –  –

6.1.4 Sub-area 4

The user requirements sub-area determined that the most feasible options are:

Location Information Cell ID (see clause 5.5.2.5) because it is a simple method that requires little standardization effort and no changes to the mobile stations, although the accuracy of the location is limited to the cell area. The standardization effort would centre on procedural additions to the standard rather than any new PDUs.

Received Signal Strength (RSS) (see clause 5.5.2.5) because although of variable accuracy by itself, when combined with Cell ID it could provide enhanced accuracy. Since its implementation would require co-ordination and signalling between base stations and hence also a moderate degree of additional standardization work, it should be studied in more detail to determine whether it would be a viable option. Note that standardization regarding the RSS measurement is proposed in Sub-area 1.

GPS Stand-alone (see clause 5.5.2.5) because it would provide the best location accuracy of the options studied and, although requiring integration of a GPS receiver into the mobile stations, with current and anticipated future levels of circuit technology it should be readily achievable with modest increase in cost. It should be noted, however, that the lengthy start-up process may preclude its use in handheld terminals for which an assisted method may be needed (see below).

GPS Network Assisted - Mobile Based (see clause 5.5.2.5) because it would provide an enhancement to stand-alone GPS enabling more rapid start-up synchronization to make GPS more feasible for use in handheld mobile stations. The need to also locate GPS receivers at base station sites which would need to transmit assistance data to mobile stations would require some standardization work.

Extended Range Every other timeslot (see clause 5.5.3.5) because it would require little enhancement to the TETRA standard.

The timing advance method (see clause 5.5.3.5) would require significant standardization effort with major impact on terminals and base stations (with backward compatibility implications) but would be more spectrally efficient.

–  –  –

6.2.1.1 Sub-area 1 options Improved Handover It is recommended that Clause 6.1.2 options 1 to 8 (inclusive) should be incorporated in phase 1. This is because they will bring the largest benefits for the least amount of standardization work.

It should be noted that several of these options are linked to power control of MSs and MS location services. These could affect the same parts of the standard and bring about improvements in those areas at the same time.

Hierarchical Cell Structures One quick win solution was identified to enable the implementation of Hierarchical Cell Structures. This is to define the "Cell Priority" element to label microcells and get them distinguished from macrocells. The values of TEMPORARY_OFFSET and PENALTY_TIME will have to be fixed in the MS at this time.

6.2.1.2 Sub-area 2 options All options should be included in phase 1 as they bring benefits with small changes to the standards (Air Interface and Codec). There are no new PDUs or air interface signalling changes only changes in some values.

The work mainly revolves around EN 300 392-2 [1], table 342, which has suggested changes from the "improved handover" clause in any case. A suggestion is to change the meaning of the power control element values in table 342.

–  –  –





Instead of "number of steps" the values could indicate "change power (up/down) by 1,2,5 or 10 dB. This gives the (signalling) capability of a 1 dB step with a large dynamic range at the same time.

The other area is the reservation of a usage marker value as a power control element in the AACH.

–  –  –

6.2.1.4 Sub-area 4 options Cell ID (see clause 5.5.2.5) because it is a simple method that requires little standardization effort and no changes to the mobile stations, although the accuracy of the location is limited to the cell area. The standardization effort would centre on procedural additions to the standard rather than any new PDUs - it is therefore considered to be a candidate for Phase 1 standardization work.

GPS Stand-alone (see clause 5.5.2.5) because it would provide the best location accuracy of the options studied and, although requiring integration of a GPS receiver into the mobile stations, with current and anticipated future levels of circuit technology it should be readily achievable with modest increase in cost. It should be noted, however, that the lengthy start-up process may preclude its use in handheld terminals for which an assisted method may be needed (see clause 6.2.2.4 below) - it is therefore considered to be a candidate for Phase 1 standardization work.

Every other timeslot (see clause 5.5.3.5) because it would require little enhancement to the TETRA standard so it is considered to be a candidate for Phase 1 standardization work.

–  –  –

6.2.2.1 Sub-area 1 options Improved Handover It is felt that Clause 6.1.1 options 9 to 15 (inclusive) should be included into phase 2. This is because work in standardization will bring about benefits in consistent behaviour and flexibility in operation of handover. The working groups must consider the half-duplex calls (individual and group) and interaction with other TG23 work such as discontinuous transmission. Both of these will affect the uplink transmission of an MS.

Hierarchical Cell Structure A more flexible solution to enable the implementation of Hierarchical Cell Structures can fit in phase 2 work. This is to add the TEMPORARY_OFFSET and PENALTY_TIME elements to the broadcast message.

Benefits would result from standardization of some sub-area 1 options which have known benefit and require more standardization/implementation work than phase 1 options.

–  –  –

6.2.2.4 Sub-area 4 options Received Signal Strength (RSS) (see clause 5.5.2.5) is considered to be a phase 2 option because, although of variable accuracy by itself, when combined with Cell ID it could provide enhanced accuracy. Since its implementation would require co-ordination and signalling between base stations and hence also a moderate degree of additional standardization work, it should be studied in more detail to determine whether it would be a viable option. Note that standardization regarding the RSS measurement is proposed in Sub-area 1 for Phase 1 work (see clause 6.2.1.4).

ETSI 43 ETSI TR 101 987 V1.1.1 (2001-08) GPS Network Assisted - Mobile Based (see clause 5.5.2.5) is considered to be a phase 2 option because it would provide an enhancement to stand-alone GPS enabling more rapid start-up synchronization to make GPS more feasible for use in handheld mobile stations. The need to also locate GPS receivers at base station sites, which would need to transmit assistance data to mobile stations, would require some standardization work.

–  –  –

6.2.3.1 Sub-area 1 options Frequency Hopping Two work streams have been identified as areas of research to determine the feasibility of Frequency Hopping in

TETRA, these are:

1) Investigate solutions to surmount the Linearization issue, which seems to be a barrier to implementing Frequency Hopping in TETRA.

2) Evaluate the benefits of FH and compare with the cost of its implementation and standardization.

–  –  –

6.2.3.4 Sub-area 4 options The timing advance method of achieving extended range (see clause 5.5.3.5) is considered to be a phase 3 option because it would require significant standardization effort with major impact on terminals and base stations (with backward compatibility implications) but would be more spectrally efficient than the every other timeslot method.

6.3 Enhancements timeline Enhancement timeline is proposed to be as defined in table 21.

–  –  –

7.1 General Some other options to enhance system performance were considered. These fall into two categories: some of them were considered unfeasible and therefore dismissed at an early stage of TG23 work. The others were not considered or studied within TG23, but believed to be worthy of studying to determine their feasibility. They can be studied as part of phase 2 or phase 3. The following two clauses list all the options in each category.

7.2 Sub-area 1 7.2.1 Unfeasible options These options were considered unfeasible at an early stage of TG23 work. Therefore, they were not pursued any further.

These options are:

• Downlink Power Control.

NOTE 1: suggested that downlink power control could reduce system interference. However, implementation issues associated with ramping power up and down on slot-by-slot basis rendered this option unfeasible.

• Modifying Interleaving Schemes for Voice Calls (Inter-frame Interleaving).

NOTE 2: This was suggested to improve the efficiency of channel coding and frequency hopping. However, inter-frame interleaving would increase speech delay. Since one of the requirements of TG23 was to reduce speech delay, inter-frame interleaving was rendered unfeasible and was not pursued any further.

7.2.2 Unstudied options Some techniques can be used to enhance system performance and improve system quality. Such techniques might have

some air interface requirements in order to be implemented. These techniques are:

1) Smart antennas.

2) Underlay/Overlay.

3) Equalizers and the use of Time Selection Diversity.

4) Directed Retry.

The impact of these techniques on the TETRA air interface was not studied within TG23. A study needs to be conducted to determine the impact of these techniques on the air interface and the feasibility of their implementation and standardization. It is suggested that this feasibility study should be in phase 2 of TETRA Release 2 work.

7.3 Sub-area 2None

7.4 Sub-area 3 7.4.1 Unfeasible Options Transmission of large segments by "Slot spanning" or "Slot Chaining" (see clause 5.4.1.4) was determined as unfeasible. The increased throughput was insufficient to justify further investigation. The retransmission of failed segments would further reduce the effective throughput on the Air Interface.

–  –  –

7.4.2 Unstudied options The following options mentioned in the "Transmission of Large PDUs" clause above were not discussed within the

TG23 forum:

• Use of advanced Link for large PDUs;

• Protocol Configuration for SNDCP.

Implementation of an Advanced Link for large PDUs is a feasible option as it is permitted within the current Air Interface standard [1] clause 24.4.2.1. This option should be considered for discussion within WG3, as it will however require agreement and discussion to ensure interoperability between different manufacturers equipment.

Enhancing the SNDCP protocol to cater for large amounts of protocol configuration data -is not covered by the current Air Interface standard [1]. The use of additional SNDCP PDUs for protocol configuration implies potential benefits where the current PDUs may become fragmented. If the protocol configuration element exceeds 128 octets then the limitation imposed by the current SNDCP protocol may need enhancing. However further study is required within WG3 to examine the full nature of the perceived problem and the benefits and costs of any proposed solutions.

7.5 Sub-area 4 7.5.1 Unfeasible options These options were considered unfeasible in the TG23 work. Therefore, they were not pursued any further. These

options are:

Timing Advance / Round Trip Time (TA / RTT) (see clause 5.52.5) because these methods would be limited to a location accuracy of 1-2 km and would incur unjustifiable implementation costs in the TETRA network.

Angle of Arrival (AoA) (see clause 5.5.2.5) because although it could potentially provide accurate location data in good propagation conditions it would require both software and hardware changes to the network and co-ordination between base stations. Since reflections and non-line of sight conditions would degrade the location accuracy it was considered that the potential, as yet unknown, benefits could not be justified by the additional standardization work and implementation costs.

Time of Arrival (TOA) and Observed Time Difference (OTD) (see clause 5.5.2.5) would not provide sufficient accuracy in location measurement compared to other methods and may require more accurate synchronization and timing resolution plus significant implementation costs. 1 - 2 km accuracy is achievable.

There were no sub-area 4 "other options" which were considered worthy of studying to determine their feasibility.

7.5.2 Unstudied options None identified.

–  –  –

Annex A:

Options vs. Requirements Matrix The following matrix has been used during the initial process of identifying options and mapping them to the requirements. It is included here for background information and should not be considered part of the report recommendations and conclusion.

–  –  –

LEGEND Improving Spectrum Efficiency, Capacity, and System Performance.

Improvement of Terminal Characteristics.

Optimization of Frame Structure and Protocols.

User requirements and potential legal requirements implementation.

–  –  –

Annex B:

Bibliography TETRA Release 2 Work Programme, EPT13(00)17r1.

Terms of Reference for TG23, EPT MC45(01)05r2.

Terms of Reference for WG2, EPT MC45(01)12r1.

Terms of Reference for WG3, EPT MC45(01)06.

Terms of Reference for the Specialist Task Force JH ("TETRA2") to support EP TETRA for the years 2001 through to 2003 in the development of TETRA "Release 2", EPT13(00)16 -ToR JHr11.

Extension of EPT Terms of Reference to Enable TETRA "Release 2" (EPT input to ETSI Board #28), ETSI/B28(00)12.

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