More on LTE-Advanced

LTE-Advanced should be real broadband wireless networks that provide equal or greater peak data rates than those for wired networks, i.e., FTTH (Fiber To The Home), while maintaining equivalent QoS. Smooth introduction of LTE-Advanced should be possible on top of LTE system.

High-level requirements
•Reduced network cost (cost per bit)
•Better service provisioning
•Compatibility with 3GPP systems

Spectrum

WRC 07 identified the following new bands for use by IMT/IMT-Advanced:

• 450−470 MHz band,
• 698−862 MHz band,
• 790−862 MHz band,
• 2.3−2.4 GHz band, and
• 3.4−3.6 GHz band.

Not all of these bands are available on a worldwide basis. These bands are in addition to the bands currently specified in 3GPP. Specification for C-band should not be restricted to 3.4 – 3.6 GHz, but cover 3.4 to 3.8 and even 3.4 to 4.2 GHz as these will likely become available in some countries.

Channel Bandwidth

• Channel bandwidths up to 100 MHz to be specified
• However, for many operators consecutive allocation of 100 MHz unlikely
• optimised performance needed for smaller bandwidths of e.g. 50 MHz low cost/complexity (i.e. not fully flexible) resource aggregation to be considered

Interworking with legacy 3GPP RAT

• Full low complexity (for NW and terminal) interworking with 3GPP RAT, so operator de facto has flexibility on technology to deploy, when and where. The networks of most operators will be a combination of multiple 3GPP RAT for many years to come.
• Network Sharing: Support for at least all currently specified Network Sharing features, also to facilitate cost-efficient roll out of LTE-Advanced, including, but not limited to, rural area coverage.

Working Methods

• As LTE-Advanced should be an evolution of LTE, it is essential that it is specified as part of the 36-series of specifications.
• It is also essential work is performed to a large degree by the experts that developed LTE, and thus work ideally should be performed in existing Working Groups.
• LTE-Advanced will likely constitute the next significant development step for LTE, but (smaller) stand-alone enhancements and additions to LTE should be possible, and progressed in parallel.
• Some of these smaller enhancements, as well as the “corrections” to LTE Release 8 could/should be captured in Rel.9, where SAE considerations will lead to relatively short Release completion time-frame.

More details on LTE-Advanced workshop in China here.

The workshop docs are available here.

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IMT Advanced = 4G

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In this story on Telecom TV, is says:

Working under a mandate to address “systems beyond 3G”, the working party has now come up with a name for the future mobile systems. Thankfully, they are veering away from 4G and are calling it ‘IMT-Advanced’.

A simple search on Google returned some useful information from Telecom ABC:

International Mobile Telecommunications – Advanced (IMT-Advanced) is a concept from the ITU for mobile communication systems with capabilities which go further than that of IMT-2000. IMT-Advanced was previously known as “systems beyond IMT-2000”.

It is foreseen that the development of IMT-2000 will reach a limit of around 30 Mbps. In the vision of the ITU, there may be a need for a new wireless access technology to be developed around the year 2010 capable of supporting even higher data rates with high mobility, which could be widely deployed around the year 2015 in some countries. The new capabilities of these IMT-Advanced systems are envisaged to handle a wide range of supported data rates according to economic and service demands in multi-user environments with target peak data rates of up to approximately 100 Mbit/s for high mobility such as mobile access and up to approximately 1 Gbit/s for low mobility such as nomadic/local wireless access.

To support this wide variety of services, it may be necessary for IMT-Advanced to have different radio interfaces and frequency bands for mobile access for highly mobile users and for new nomadic/local area wireless access.

Together with the introduction of the name IMT-Advanced, the ITU introduced the generic root name IMT. The generic root name IMT covers the capabilities of IMT-2000, including future development of IMT-2000, and IMT-Advanced.

Meanwhile a story in ChinaTechNews is suggesting that Datang Telecom has already written a Draft on 4G and is working on 3G&4G convergence. Cannot find much more on this right now.

For more on 4G technologies, either read this story on Network World or 3G4G website.

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Multiuser Cooperative Diversity and Virtual MIMO

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MIMO (Multiple Input Multiple Output) by definition requires multiple antenna but it is also possible to use one antenna with Co-operative Diversity to create Cooperative MIMO or Virtual MIMO.

Earlier this year, Nokia Siemens Network reported the following on Virtual MIMO:

Researchers at Nokia Siemens Networks have demonstrated in lab conditions how a virtual Multiple Input Multiple Output (MIMO) technique can be used for the uplink in LTE (Long Term Evolution) networks.

Tests at its labs in Munich, Germany, have shown how, using such an SDMA (Space Division Multiple Access) based technique, two standard mobile devices, each with only one physical transmission antenna, can communicate with a base station simultaneously and on the same radio channel.

On the uplink transmission, data rates of 108Mbit/s were achieved, double the usual speed, while the downlink managed 160Mbit/s.

The researchers say that while MIMO on the downlink primarily generates higher peak data rates for the end user, virtual MIMO on the uplink makes it possible for an operator to increase network capacity and better utilize the available spectrum.

Nokia Siemens also said the technique contributes to one of the crucial prerequisites for the success of LTE by reducing power consumption of LTE based devices to “acceptable levels” even when used for very high data-intensive applications and that this should be achieved at “moderate prices.”

The researchers say that with virtual MIMO only one power amplifier and transmission antenna is necessary for each device, contributing to reduced production costs and power needs.

In the LTE test bed, developed and built in collaboration with the Fraunhofer Institute for Telecommunications (Heinrich Hertz Institute), two co-operating end-user devices form a virtual MIMO system in which the antenna elements are distributed over the two devices. The two devices can be supplied simultaneously with data over the same frequency band using space division multiplexing.

The following is an extract from EURASIP Journal onWireless Communications and Networking:

Multihop relaying technology is a promising solution for future cellular and ad hoc wireless communications systems in order to achieve broader coverage and to mitigate wireless channels impairment without the need to use high power at the transmitter.

Recently, a new concept that is being actively studied in multihop-augmented networks is multiuser cooperativediversity, where several terminals forma kind of coalition to assist each other with the transmission of their messages.

In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version to the intended destination node. The destination node combines the signal received from the relays, possibly also taking into account the source’s original signal.

Cooperative diversity exploits two fundamentals features of wireless medium: its broadcast nature and its ability to achieve diversity through independent channels.

There are three advantages from this:

(1) Diversity. This occurs because different paths are likely to fade independently. The impact of this is expected to be seen in the physical layer, in the design of a receiver that can exploit this diversity.

(2) Beamforming gain. The use of directed beams should improve the capacity on the individual wireless links.The gains may be particularly significant if space-time coding schemes are used.

(3) Interference mitigation. A protocol that takes advantage of the wireless channel and the antennas and receivers available could achieve a substantial gain in system throughput by optimizing the processing done inthe cooperative relays and in the scheduling of retransmissions by the relays so as to minimize mutual interference and facilitate information transmission by cooperation.

Source: Multiuser Cooperative Diversity forWireless Networks by George K. Karagiannidis, Chintha Tellambura, Sayandev Mukherjee and Abraham O. Fapojuwo, Volume 2006, Article ID 17202

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LTE in few words

Before it gets out from my mind. People keep on asking what LTE is without going in the details. So here it is:

3G LTE, as proposed in 3GPP Release 8, aims to increase cell data capacity by at least five times over the current implementations of HSPA. It will support more users per cell, as well as higher speeds to individual users, and is intended to match DSL speeds currently available to the home. A simplified protocol structure and re-definition of the functional split between network elements and basestations is intended to raise efficiency while making all VoIP networks possible.

Some of the highlights of LTE are:

• OFDM-based air interface (Orthogonal Frequency Division Multiplexing) … WCDMA is out.
• Channel bandwidths from 1.25 to 20MHz are supported
• Increased spectrum efficiency and peak data rates at cell edge.
• Target peak rates of 100 Mbps/DL and 50 Mbps/UL. (Nokia-Siemens have already achieved 108Mbps though)
• Increased spectrum efficiency and peak data rates at cell edge.
• Reduced latency for both user and control plane: less than 10ms round trip delay for user plane between UE and the serving RAN node, less than 100ms transition time for control plane between inactive state and active state.
• Support for diversity and MIMO

The first LTE-based networks are expected to roll out in 2009/2010. In contrast to other cellular technologies, conformance tests for LTE are expected to be available more than two years ahead of any service introduction according to Agilent. This will ensure user devices are available in volume when the network services are finally launched.

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Is UMB the same as LTE

Recently i have come across press releases trying to sell UMB (Ultra Mobile Broadband) as 4G technology. This is the same as trying to sell LTE and mobile -WiMAX as a 4G technology.

IMT has taken a clever approach and instead of calling the successor of 3G as 4G, they are calling it IMT-Advanced.

The main requirements for 4G are as follows:

• Peak data rate of 100Mbps for high mobility applications such as mobile access
• Approx. 1Gbps for low mobility applications such as nomadic/local wireless access

Doing some digging on the UMB topic, i realised that it is the same as LTE but an evolution from CDMA2000. This is being standardised by 3GPP2.

Some of the key features (and comparing it with LTE) includes:

• It used OFDMA based air interface (same as LTE)
• It supports FDD (LTE supports FDD and TDD and a combination of them so i am not sure if UMB only supports FDD)
• Scalable b/w of 1.25MHz to 20MHz (same as LTE)
• MIMO and Beamforming (Same as LTE but UMB also supports 4×4 antennas whereas LTE supports 2×2)
• Data speeds upto 275Mbps in DL and 75Mbps in UL (LTE has 144Mbps in DL and 57Mbps in UL but that is because of 2×2 MIMO)

Since the term 4G is already being abused so much, one option is to let people use 4G as they wish and then when IMT-Advanced is available, start calling it 5G. What do you think?