3G LTE Tutorial - 3GPP Long Term Evolution

- information, overview, or tutorial about the basics of the 3GPP / 3G LTE, the long term evolution plans for the next generation of cellular telecommunications services

This 3G LTE tutorial is split into several pages each of which addresses a different aspect of 3GPP LTE technology and operation:

[1] 3G LTE Tutorial Introduction
[2] LTE OFDM and OFDMA / SC-FDMA
[3] LTE MIMO
[4] LTE TDD and FDD duplex schemes
[5] LTE frame and subframe structure
[6] LTE physical logical and transport channels
[7] LTE frequency bands and spectrum
[8] LTE SAE system architecture evolution
[9] Voice over LTE, VoLTE

With services such as WiMAX offering very high data speeds, work on developing the next generation of cellular technology has started. The UMTS cellular technology upgrade has been dubbed LTE - Long Term Evolution. The idea is that 3G LTE will enable much higher speeds to be achieved along with much lower packet latency (a growing requirement for many services these days), and that 3GPP LTE will enable cellular communications services to move forward to meet the needs for cellular technology to 2017 and well beyond.

HSPA (High Speed Packet Access), 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 stages 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 started 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 cost 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 rates of 100Mbps, and upload rates of 50Mbps 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 / 3GPP 3G standards. Although it uses a different form of radio interface, using OFDMA / 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.

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.

3G LTE technologies

LTE has introduced a number of new technologies when compared to the previous cellular systems. They enable LTE to be able to operate 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 Multiplex):   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.
• MIMO (Multiple Input Multiple Output):   One of the main problems that previous telecommunications systems has encountered is that of multiple signals arising from the many reflections that are encountered. By using MIMO, these additional signal paths can be used to advantage and are able to be used to increase the throughput.
  
  When using MIMO, it is necessary to use multiple antennas to enable the different paths to be distinguished. Accordingly schemes using 2 x 2, 4 x 2, or 4 x 4 antenna matrices can be used. While it is relatively easy to add further antennas to a base station, the same is not true of mobile handsets, where the dimensions of the user equipment limit the number of antennas which should be place at least a half wavelength apart.
• 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 can be routed more directly to its destination.

These technologies are addressed in much greater detail in the following pages of this tutorial.

3G LTE specification overview

It is worth summarizing the key parameters of the 3G LTE specification. In view of the fact that there are a number of differences between the operation of the uplink and downlink, these naturally differ in the performance they can offer.

These LTE highlight specifications give an overall view of the performance that LTE will offer. It meets the requirements 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.

3G LTE summary

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.

Further pages from this tutorial
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