LTE Advanced: NSN Proves relaying technology

Nokia Siemens Networks has broken new ground with another technological first: mobile broadband communications beyond LTE. Company researchers have successfully demonstrated Relaying technology proposed for LTE-Advanced, enabling an exceptional end-user experience delivered consistently across the network.

Completed in Nokia Siemens Networks research facilities in Germany, the demonstration illustrated how advances to Relaying technology can further improve the quality and coverage consistency of a network at the cell edge – where users are furthest from the mobile broadband base station.

Relaying technology, which can also be integrated in normal base station platforms, is cost efficient and easy to deploy as it does not require additional backhaul. The demonstration of LTE Advanced means operators can plan their LTE network investments knowing that the already best-in-class LTE radio performance, including cell edge data rates, can be further improved and that the technological development path for the next stage of LTE is secure and future-proof.

These performance enhancements have been achieved by combining an LTE system supporting a 2×2 MIMO (Multiple Input Multiple Output) antenna system, and a Relay station. The Relaying operates in-band, which means that the relay stations inserted in the network do not need an external data backhaul. They are connected to the nearest base stations by using radio resources within the operating frequency band of the base station itself. Towards the terminal they are base stations and offer the full functionality of LTE. LTE-Advanced is currently being studied by 3GPP for Release 10 and will be submitted towards ITU-R as the 3GPP Radio Interface Technology proposal.

The improved cell coverage and system fairness – meaning offering higher user data rates for and fair treatment of users distant from the base station – will allow operators to utilise existing LTE network infrastructure and still meet growing bandwidth demands.

The demonstration has been realised by using an intelligent demo relay node embedded in a test network forming a FDD in-band self-backhauling solution for coverage enhancements. With this demonstration the performance at the cell edge could be increased up to 50% of the peak throughput.

More info on LTE-A coming soon.

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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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