Long Term Evolution of the 3GPP radio technology Part 2

In adddition, the Next Generation Mobile Networks (NGMN) initiative, led by seven network operators (*) provided a set of recommendations for the creation of networks suitable for the competitive delivery of mobile broadband services. The NGMN goal is "to provide a coherent vision for technology evolution beyond 3G for the competitive delivery of broadband wireless services".


The NGMN long-term objective is to "establish clear performance targets, fundamental recommendations and deployment scenarios for a future wide area mobile broadband network". In a white paper (March 2006), they provided relative priorities of key system characteristics, System recommendations and detailed requirements.



Emphase was also on the IPR side, where the goal was "to adapt the existing IPR regime to provide a better predictability of the IPR licenses (...) to ensure Fair, Reasonable And Non-Discriminatory (FRAND) IPR costs" (NGMN White paper, March 2006).

All RAN WGs participated in the study, with collaboration from SA WG2 in the key area of the network architecture. The first part of the study resulted in agreement on the requirements for the Evolved UTRAN.



As a result, Technical Report (TR) 25.913 contains detailed requirements for the following criteria:

Peak data rate

* Instantaneous downlink peak data rate of 100 Mb/s within a 20 MHz downlink spectrum allocation (5 bps/Hz)
* Instantaneous uplink peak data rate of 50 Mb/s (2.5 bps/Hz) within a 20MHz uplink spectrum allocation)

Control-plane latency

* Transition time of less than 100 ms from a camped state, such as Release 6 Idle Mode, to an active state such as Release 6 CELL_DCH
* Transition time of less than 50 ms between a dormant state such as Release 6 CELL_PCH and an active state such as Release 6 CELL_DCH

Control-plane capacity

* At least 200 users per cell should be supported in the active state for spectrum allocations up to 5 MHz

User-plane latency

* Less than 5 ms in unload condition (ie single user with single data stream) for small IP packet

User throughput

* Downlink: average user throughput per MHz, 3 to 4 times Release 6 HSDPA
* Uplink: average user throughput per MHz, 2 to 3 times Release 6 Enhanced Uplink

Spectrum efficiency

* Downlink: In a loaded network, target for spectrum efficiency (bits/sec/Hz/site), 3 to 4 times Release 6 HSDPA )
* Uplink: In a loaded network, target for spectrum efficiency (bits/sec/Hz/site), 2 to 3 times Release 6 Enhanced Uplink

Mobility

* E-UTRAN should be optimized for low mobile speed from 0 to 15 km/h
* Higher mobile speed between 15 and 120 km/h should be supported with high performance
* Mobility across the cellular network shall be maintained at speeds from 120 km/h to 350 km/h (or even up to 500 km/h depending on the frequency band)

Coverage

* Throughput, spectrum efficiency and mobility targets above should be met for 5 km cells, and with a slight degradation for 30 km cells. Cells range up to 100 km should not be precluded.

Further Enhanced Multimedia Broadcast Multicast Service (MBMS)

* While reducing terminal complexity: same modulation, coding, multiple access approaches and UE bandwidth than for unicast operation.
* Provision of simultaneous dedicated voice and MBMS services to the user.
* Available for paired and unpaired spectrum arrangements.

Spectrum flexibility

* E-UTRA shall operate in spectrum allocations of different sizes, including 1.25 MHz, 1.6 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz in both the uplink and downlink. Operation in paired and unpaired spectrum shall be supported
* The system shall be able to support content delivery over an aggregation of resources including Radio Band Resources (as well as power, adaptive scheduling, etc) in the same and different bands, in both uplink and downlink and in both adjacent and non-adjacent channel arrangements. A “Radio Band Resource” is defined as all spectrum available to an operator

Co-existence and Inter-working with 3GPP Radio Access Technology (RAT)

* Co-existence in the same geographical area and co-location with GERAN/UTRAN on adjacent channels.
* E-UTRAN terminals supporting also UTRAN and/or GERAN operation should be able to support measurement of, and handover from and to, both 3GPP UTRAN and 3GPP GERAN.
* The interruption time during a handover of real-time services between E-UTRAN and UTRAN (or GERAN) should be less than 300 msec.

Architecture and migration

* Single E-UTRAN architecture
* The E-UTRAN architecture shall be packet based, although provision should be made to support systems supporting real-time and conversational class traffic
* E-UTRAN architecture shall minimize the presence of "single points of failure"
* E-UTRAN architecture shall support an end-to-end QoS
* Backhaul communication protocols should be optimised

Radio Resource Management requirements

* Enhanced support for end to end QoS
* Efficient support for transmission of higher layers
* Support of load sharing and policy management across different Radio Access Technologies

Complexity

* Minimize the number of options
* No redundant mandatory features

As a consequence the WGs have dedicated normal meeting time to the Evolution activity, as well as separate ad hoc meetings.

RAN WG1 assessed six possible radio interface schemes (evaluations of these technologies against the requirements for the physical layer are collected in TR 25.814).

The wide set of options initially identified by the early LTE work was narrowed down, in December 2005, to a working assumption that the downlink would use Orthogonal Frequency Division Multiplexing (OFDM) and the uplink would use Single Carrier – Frequency Division Multiple Access (SC-FDMA). Although opinions were divided, it was eventually concluded that inter-Node-B macro-diversity would not be employed. More information is given in the report of RAN#30.

Supported downlink data-modulation schemes are QPSK, 16QAM, and 64QAM. The possible uplink data-modulation schemes are (pi/2-shift) BPSK, QPSK, 8PSK and 16QAM.

The use of Multiple Input Multiple Output (MIMO) scheme was agreed, with possibly up to four antennas at the mobile side, and four antennas at the Cell site.

Re-using the expertise from the UTRAN, the same channel coding type than for UTRAN was agreed (turbo codes).

RAN WG2 has also held a first meeting to approach the radio interface protocols of the Evolved UTRAN (link). The initial assumptions were:

* Simplification of the protocol architecture and the actual protocols
* No dedicated channels, and hence a simplified MAC layer (without MAC-d entity)

* Avoiding similar functions between Radio and Core network.

A Transmission Time Interval (TTI) of 1ms was agreed (to reduce signalling overhead and improve efficiency).