HSPA, a combination of HSDPA and HSUPA, and HSPA+ are now being deployed, the 3G LTE development is being dubbed 3.99G as it is not a full 4G standard, although in reality there are many similarities with the cellular technologies being touted for the use of 4G. However, regardless of the terminology, it is certain that 3G LTE will offer significant improvements in performance over the existing 3G standards.
Many operators have not yet upgraded their basic 3G networks, and 3GPP LTE is seen as the next logical step for many operators, who will leapfrog straight from basic 3G straight to LTE as this will avoid providing several stage of upgrade. The use of LTE will also provide the data capabilities that will be required for many years and until the full launch of the full 4G standards known as LTE Advanced.
3G LTE beginnings
3GPP, the Third Generation Partnership Project that oversaw the development of the UMTS 3G system stared the work on the evolution of the 3G cellular technology with a workshop that was held in Toronto Canada in November 2004. The work on 3G LTE started with a feasibility study started in December 2004, which was finalised for inclusion on 3GPP release 7. LTE core specifications were then included in release 8.
The workshop set down a number of high level requirements for 3G LTE:
- Reduced case per bit
- Increased service provisioning - more services at lower cost with better user experience
- Flexibility of use of existing and new frequency bands
- Simplified architecture, Open interfaces
- Allow for reasonable terminal power consumption
In terms of actual figures, targets for LTE included download rate of 100Mbps, and upload rates of 5oMbps for every 20MHz of spectrum. In addition to this LTE was required to support at least 200 active users in every 5MHz cell. (i.e. 200 active phone calls). Targets have also been set for the latency in IP packet delivery. With the growing use of services including VoIP, gaming and many other applications where latency is of concern, figures need to be set for this. As a result a figure of sub-10ms latency for small IP packets has been set.
3G LTE evolution
Although there are major step changes between LTE and its 3P predecessors, it is nevertheless
looked upon as an evolution of the UMTS/SC-FDMA instead of CDMA, there are many similarities with the earlier forms of 3G architecture and there is scope for much re-use.
LTE can be seen for provide a further evolution of functionality, increased speeds and general improved performance.
3G LTE evolution
Although there are major step changes between LTE and its 3P predecessors, it is nevertheless
looked upon as an evolution of the UMTS/SC-FDMA instead of CDMA, there are many similarities with the earlier forms of 3G architecture and there is scope for much re-use.
LTE can be seen for provide a further evolution of functionality, increased speeds and general improved performance.
| WCDMA (UMTS) | HSPA HSDPA / HSUPA | HSPA+ | LTE | |
|---|---|---|---|---|
| Max downlink speed bps | 384 k | 14 M | 28 M | 100M |
| Max uplink speed bps | 128 k | 5.7 M | 11 M | 50 M |
| Latency round trip time approx | 150 ms | 100 ms | 50ms (max) | ~10 ms |
| 3GPP releases | Rel 99/4 | Rel 5 / 6 | Rel 7 | Rel 8 |
| Approx years of initial roll out | 2003 / 4 | 2005 / 6 HSDPA 2007 / 8 HSUPA | 2008 / 9 | 2009 / 10 |
| Access methodology | CDMA | CDMA | CDMA | OFDMA / SC-FDMA |
In addition to this, LTE is an all IP based network, supporting both IPv4 and IPv6. There is also no basic provision for voice, although this can be carried as VoiP.
LTE has introduced a number of new technologies when compared to the previous cellular systems. They enable LTE be able to operated more efficiently with respect to the use of spectrum, and also to provide the much higher data rates that are being required
- OFDM(Orthogonal Frequency Division Mulitplex): OFDM technology has been incorporated into LTE because it enables high data bandwidths to be transmitted efficiently while still providing a high degree of resilience to reflections and interference. The access schemes differ between the uplink and downlink: OFDMA(Orthogonal Frequency Division Multiple Access is used in the downlink); while SC-FDMA(Single Carrier - Frequency Division Multiple Access) is used in the uplink. SC-FDMA is used in view of the fact that its peak to average power ratio is small and the more constant power enables high RF power amplifier efficiency in the mobile handsets - an important factor for battery power equipment.
- MINO(Multiple Input Multiple Output): One of the main problems that previous telecommunications systems has encountered is that of multiple signals arsing from the many reflections that are encountered. By using MIMO, there additional signal paths can be used to advantage and are able to be used to increase the throughput
- SAE( system Architecture Evolution): With the very high data rate and low latency requirements for 3G LTE, it is necessary to evolve the system architecture to enable the improved performance to be achieved. One change is that a number of the functions previously handled by the core network have been transferred out to the periphery. Essentially this provides a much "flatter" form of network architecture. In this way latency times can be reduced and data rate can be routed more directly to its destination.
3G LTE specification overview
It is worth summarizing the key parameters of the3G LTE specification. In view of the fact that there are a number of differences between the operation of the uplink and downlink, there naturally differ in the performance they can offer.
| PARAMETER | DETAILS |
|---|---|
| Peak downlink speed 64QAM (Mbps) | 100 (SISO), 172 (2x2 MIMO), 326 (4x4 MIMO) |
| Peak uplink speeds (Mbps) | 50 (QPSK), 57 (16QAM), 86 (64QAM) |
| Data type | All packet switched data (voice and data). No circuit switched. |
| Channel bandwidths (MHz) | 1.4, 3, 5, 10, 15, 20 |
| Duplex schemes | FDD and TDD |
| Mobility | 0 - 15 km/h (optimised), 15 - 120 km/h (high performance) |
| Latency | Idle to active less than 100ms Small packets ~10 ms |
| Spectral efficiency | Downlink: 3 - 4 times Rel 6 HSDPA Uplink: 2 -3 x Rel 6 HSUPA |
| Access schemes | OFDMA (Downlink) SC-FDMA (Uplink) |
| Modulation types supported | QPSK, 16QAM, 64QAM (Uplink and downlink) |
There LTE highlight specifications give anoverall view of the performance that LTE will offer. It meets therequirements of industry for high data download speeds as well as reduced latency - a factor important for many applications from VoIP to gaming and interactive use of data. It also provides significant improvements in the use of the available spectrum
The basic work on 3G LTE has now been completed by 3GPP, although the initial drafts were released in September 2007 and the parallel work on the infrastructure technology known as LTE System Architecture Evolution (SAE) followed shortly afterwards. In terms of the deployments of real systems some anticipate that the first deployments may be seen in 2010 although one of the main problems will be the user equipment. Initially these are likely to consist of broadband "dongles" for use with laptops with other mobiles appearing later.
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