3G Long-Term Evolution - Testing Times. Long Term Evolution Status. Early Challenges

3G Long-Term Evolution - Testing Times

Radio-Electronics Magazine, September 2008, Test and measurement.

Evan Gray of the Wireless Division, Aeroflex Test Solutions describes how testing LTE and the test solutions that are available will play a key part in the development of LTE by feeding back vital information into the development. 

GSM/3GSM radio access technology dominates today’s global cellular landscape with over 2.5 billion users and this figure is steadily rising. To keep pace with this growth, and the demand for even faster, more bandwidth-intensive mobile telecommunications services, it is essential that the infrastructure technology continues to evolve to become more efficient. The key to sustaining this success is the development of the underpinning technology. The responsibility for defining this lies with the 3GPP standards forum. For past three years 3GPP has been specifying the next major evolution of the GSM/UMTS standards. This evolution has two threads: The first is the enhancement of the existing WCDMA Universal Terrestrial Radio Access Network, UTRAN, through the High Speed Packet Access Plus, HSPA+, specifications. The second  is the Long Term Evolution, LTE, specifications for the Evolved Universal Terrestrial Radio Access Network, E-UTRAN. This also includes an evolution of the underlying core network in a development known as System Architecture Evolution, SAE.

Long Term Evolution Status

HSPA technology is now firmly established as a technology and as a commercial reality. There are over 120 networks delivering broadband mobile capability and more than 300 different device types.  HSPA+ will access the remaining potential of the existing 5MHz WCDMA radio access networks, offering peak data rates up to three times that of HSPA as well as improved response times. Long Term Evolution, LTE, together with the associated System Architecture Evolution, SAE, will provide a step improvement to the capabilities of the system. It will deliver peak data rates of 300Mbps in the downlink and up to 75Mbps in the uplink, as well as providing a faster response through reduced latency.  The LTE/SAE specifications define a new radio interface as well as a simplified, optimized, all-IP core network. These will provide a higher level of spectral efficiency and flexibility, higher numbers of users per cell and lower per-Mbyte cost. The LTE/SAE network architecture will also accommodate the co-existence and interoperation with other Radio Access Technologies including GERAN/UTRAN and even WiMAX. Much of the radio spectrum required for Long Term Evolution, LTE will come from 3G extension bands and GSM spectrum “re-farming.” This radio spectrum is fragmented being spread over a wide frequency range from 400MHz to over 3 GHz. 3G LTE specifications will address this issue of diverse allocations of radio spectrum resource through support of variable RF bandwidths (ranging from 1.25MHz up to 20MHz), paired and unpaired frequencies and multiple RF bands.

Other radio access technology changes employed in the long term evolution are the adoption of OFDMA (Orthogonal frequency-division multiple access (OFDMA), and increased spectral efficiency from multiple antenna (MIMO) technology and higher order modulations. The demanding pace of standards development has so far yielded the specification at around 90% of the fundamental layers of the 3G LTE Radio Access Network (RAN).  Major milestone was achieved in January 2008 when these specifications received approval for inclusion into the 3GPP Release 8 standards. Progress has been no less impressive on the implementation side with several long term evolution experimental demonstrations and pre-commercial trials already under way and major new trials due to run in 2008. Aeroflex supports a number of these programs and general LTE test and testing through its TM500 LTE test mobile and PXI waveform generator solutions. This momentum bodes well for the roll out of the first 3GPP LTE commercial systems, forecast to start in early 2010. In the meantime, 3GPP HSPA+ is expected to enable operators to offer early access to evolved services as well as facilitating a smooth transition to 3G LTE. It ensures that there is no competitive gap between today’s HSPA and future 3G LTE networks.

Early Challenges

Significant progress has been made in establishing the first formal 3GPP LTE RAN specifications and early proof of concept trials. However there are still plenty of challenges ahead. The completion of the specifications, followed by implementation, test and initial roll out of commercial systems will continue to require huge efforts from the cellular industry. In these early stages, the fast pace of development, implementation of a new air interface and the architectural changes in the RAN are likely to be demanding.