I thought this was sort of interesting from the 3GPP LTE evaluation. This report seems to support Q's claims....and while Q is one of the sources for this, so is Cingular, 3, Ericsson and Huawei.
Summary....there is no difference in the efficiency of OFDM vs. CDMA. The CDMA path requires more complex receivers, but only with channels above 20MHz or "high-order" MIMO antennas.
Document 050879
ftp://ftp.3gpp.org/tsg_ran/TSG_RAN/TSGR_30/Docs/
3GPP TSG-RAN #30 RP-050879
Nov 29th – Dec 2nd, 2005
St-Julian, Malta
Agenda item: 8.18.3.4
Source: Cingular Wireless, 3, TeliaSonera, RITT, CMCC, CATT, Ericsson, QUALCOMM Europe, Huawei
Title: Way forward on UTRA Evolution and E-UTRA Development
Document for: Discussion & Decision
1. Introduction
At RAN1 #43, the following conclusions were made regarding the E-UTRA multiple-access scheme as documented in RAN #30, RP 050758.
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There was a strong desire from the clear majority of the meeting for the same MA scheme for paired and unpaired spectrum operation as also indicated by the requirements in TR 25.913.
- The concepts fulfilling the above requirement are:
o SC-FDMA UL, OFDM DL (as proposed by 23 companies in R1-051577)
o Proposal based on MC-(W)CDMA supported by a small number of companies
- Other proposal (OFDM UL TDD, OFDM DL TDD&FDD, SC-FDMA UL FDD), thus with different MA scheme for paired and unpaired spectrum operation, were objected by a big majority of the meeting
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The two concepts mentioned above (OFDM / SC-FDMA and MC-(W)CDMA) can be seen as two different approaches to the 3GPP radio-access evolution:
- OFDM/SC-FDMA implies, at least in terms of Layer 1 and MAC , a new radio-access technology with primary focus on optimal fulfilment of the performance requirements envisioned for the long-term 3G evolution and, at the same time, limited a priori constraints on the air-interface design.
- MC-WCDMA implies a more “evolutionary” approach, also in terms of Layer 1, with a stronger emphasis on backwards compatibility, e.g. in terms of spectrum usage and reuse of technology.
2. Technical summary
Based on the evaluations carried out within RAN1 (summarized in TR 25.814), the following conclusions can be drawn:
- Based on the initial system-level evaluations there seems to be no substantial difference in the basic spectral efficiency [bps/Hz/cell] achievable with a (CDMA-based) system according to the “evolutionary” approach vs. a new (e.g. OFDM-based) Layer 1, assuming similar antenna arrangements and state-of-the-art receiver structures for a CDMA-based system
- Although UE receiver processing can be assumed to be somewhat simpler for a downlink OFDMA-based air interface, the difference in the overall receiver complexity becomes significant only when considering larger (e.g. 20 MHz) bandwidths and/or high order MIMO configurations.
- A new Layer 1, with an inherent avoidance of a priori constraints in the air-interface design, allows for a freer choice of design parameters, making it easier to fulfil some of the E-UTRA targets e.g. latency requirements, finer minimum bandwidth granularity, commonality between different duplex modes, etc.
- On the other hand, a more “evolutionary” approach enables a smoother migration of current 3G spectrum including possibility for spectrum sharing with existing UTRA releases.
Thus one could fairly state that both approaches to the 3GPP radio-access evolution have their advantages and disadvantages, very much depending on the exact scenario.
3. Proposed way forward
In order to proceed with the LTE work according to the agreed upon work plan, we propose that in this meeting:
• 3GPP RAN should note in the meeting report that the existing UTRA modes (WCDMA as well as TD-(S)CDMA) and further evolutions of these, offer and will continue to offer, a very competitive platform for operation in 5 MHz allocations.
• 3GPP RAN should affirm that TSG-RAN will continue to evolve the existing UTRA modes; this includes but is not limited to: definition of additional sets of demodulation performance requirements based on further advanced receivers in the UE and in the Node-B, support for more advanced multi-antenna solutions including MIMO, improved support for broadcast services, improved support for real time services such as IMS VoIP and gaming , protocol and architecture improvements for reduced latency, reduced call-set-up times, and improved QoS, etc.
• 3GPP RAN should include the text in Section 2 above in TR 25.814 to document the rationale for both evolution of UTRA and the development of E-UTRA as necessary work.
• 3GPP RAN should decide to proceed with the Long-Term Evolution feasibility study assuming OFDMA as the downlink multiple access technique and SC-FDMA as the uplink multiple access technique and therefore approve the text proposal attached to document RAN #30 RP 050758 from RAN WG1. |
