UMB Ultra-Mobile Broadband

Ultra-Mobile Broadband, UMB is the name for the next evolution for the cdma2000 cellular telecommunications system which is run under the auspices of 3GPP2. The UMB cellular system promises to provide very much faster data transfer speeds, and enables the system to compete with other mobile broadband systems including WiMAX and Wi-Fi.

The aims for UMB, Ultra-Mobile Broadband include making significant increases to the user data rates when compared to the existing cdma2000 cellular technologies, there will be increases to the system capacity, a lowering the cost per bit of data transfer, enhancements to the existing services, possibility of new applications, and the ability to use new spectrum opportunities.While UMB was viewed as the major evolution for cdma2000, Qualcomm, a major supporter withdrew their support in November 2008 as few operators were planning to utilise the system. Instead Qualcomm put their efforts behind the 3GPP based LTE - Long Term Evolution format that was being proposed as the global standard by many. Although some companies did continue their development for a while, the UMB standard is not expected to be deployed, at least in any large scale manner.

UMB salient features

The UMB, Ultra-Mobile Broadband cellular telecommunications system offers has many new features and techniques that enable it to fulfil the high expectations for it, and to enable it to compete with other new and emerging technologies.

• Data rates of over 275 Mbit/s in the downlink (base station to mobile) and over 75 Mbit/s in the uplink (mobile to base station).
• Uses an OFDM / OFDMA air interface
• Uses frequency division duplex (FDD).
• Possesses an IP network architecture
• Has a scalable bandwidth between 1.25 - 20 MHz (NB - OFDM / OFDMA systems are well suited for wide and scalable bandwidths)
• Supports flat, mixed and distributed network architectures

It can be seen from the features and salient points, that the UMB cellular system will provide a significant leap in terms of capability when compared to the existing cdma2000 based systems. However UMB will operate alongside cdam2000 1X and cdma2000 1X-EVDO, and it will offer seamless handoff to and from these services. In this way a phased roll-out of the new UMB service can be offered.

UMB air interface

There are a number of new technologies being used within the air interface of UMB. One of the key technologies is OFDM, Orthogonal Frequency Division Multiplex. The use of OFDM offers UMB the ability to carry high data rates as well as providing the ability to use wide and variable bandwidths according to the requirements of the link.

Note on OFDM:

Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each another there is no mutual interference. This is achieved by having the carrier spacing equal to the reciprocal of the symbol period. This means that when the signals are demodulated they will have a whole number of cycles in the symbol period and their contribution will sum to zero - in other words there is no interference contribution. The data to be transmitted is split across all the carriers and this means that by using error correction techniques, if some of the carriers are lost due to multi-path effects, then the data can be reconstructed. Additionally having data carried at a low rate across all the carriers means that the effects of reflections and inter-symbol interference can be overcome. It also means that single frequency networks, where all transmitters can transmit on the same channel can be implemented.

Click on the link for an OFDM tutorial

OFDMA, or orthogonal frequency division multiple access uses OFDM as the basis of the modulation scheme, but it has been modified for cellular telecommunications systems including UMB to provide a means of multiple access. In this way it is possible for UMB to benefit from the advantages of UMB in terms of its resilience to multipath effects while still being able to provide a means of access to multiple users.

MIMO for UMB

In addition to introducing the use of OFDM for UMB, the system also uses MIMO, Multiple Input Multiple Output (MIMO) as well as SDMA, Space Division Multiple Access. These are advanced antenna techniques to provide even greater capacity, coverage, and quality in deployments with multiple antennas. By using the multiple paths present in any real radio path, they effectively enable the channel capacity to be increased way beyond that predicted for the use of a single path for that channel.

Note on MIMO:

Two major limitations in communications channels can be multipath interference, and the data throughput limitations as a result of Shannon's Law. MIMO provides a way of utilising the multiple signal paths that exist between a transmitter and receiver to significantly improve the data throughput available on a given channel with its defined bandwidth. By using multiple antennas at the transmitter and receiver along with some complex digital signal processing, MIMO technology enables the system to set up multiple data streams on the same channel, thereby increasing the data capacity of a channel.

Click on the link for a MIMO tutorial

UMB Higher layers

The new UMB standard utilises sophisticated control mechanisms along with MIMO, and SDMA to allow the transmission of variable length packets for each application based upon the end-to-end system capabilities and the quality of service (QoS). In this way the system can be optimised according to the prevailing conditions and the requirements of each user.

To ease the introduction and roll-out of UMB, the system inter-technology hand-offs to and from existing CDMA2000 1X and 1xEV-DO systems.

UMB IP based structure

In line with the move packet based data and IP (Internet Protocol), UMB is following this trend. Its architecture has been drawn up to be able to support a large variety of services that require extremely low latencies, low jitter and increased spectral efficiencies. As a result, UMB is able to support a large cross-section of advanced mobile broadband services by delivering low rate, low latency, voice traffic at one end of the spectrum, and ultra-high-speed, latency insensitive, broadband data traffic at the other. In this way it is able to offer a better performance for many of the new services being conceived.

UMB summary

With UMB developments now moving ahead apace, news of the new technology will start to appear increasingly within the literature. Although UMB, Ultra-Mobile Broadband services are now due to be deployed until 2009, many preparations will need to be made for UMB before this.