LTE’s Role in Enabling the Future of Data Services

By Renaud Duverne, Marketing Initiative Manager, Agilent Technologies.

Introduction

The availability of data services is now being eyed by mobile operators as a key way to increase user revenue. In particular, some of the services to benefit from higher data rates include ringtones, music downloads, video calls, and TV services. The problem, of course is that today mobile networks are all about voice services with only a small proportion of users (e.g., roughly 10% in developed areas, less in developing markets) using any data capability at all other than Short Message Service (SMS) to send short text messages to mobile phones. “Real” data usage is likely even less since most operators include SMS in their data services statistics.

It seems then, that the only way to make more profit off voice services is to increase efficiency – call charges are increasingly competitive and usage is growing at the expense of wired networks. And, any enhancements aimed at increasing data usage need to ensure that there's no compromise in voice service quality or availability.

Apart from purely technical decisions, operators must also determine how to deliver services that will encourage users to upgrade to devices supporting both new and legacy technologies seamlessly, for both operation and billing. Consider, for example, that the evolution from mobile networks which supported voice-only calls to those that support data services began with GPRS. However, transfer speeds were too slow to support a comfortable user experience and early service take‑up was disappointing. Today, new generations of phones support multiple technologies – typically EGPRS, GSM and W-CDMA - as well as connectivity via Bluetooth and possibly WLAN. The first HSPA devices are also now coming to market, raising potential download speeds to around 1 Mbps.

An Emerging Solution

The Long Term Evolution (LTE) proposed in 3GPP Release 8 aims to increase cell data capacity by at least 5 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 the DSL speeds currently available to the home. A simplified protocol structure and re-definition of the functional split between network elements and base stations is intended to raise efficiency while making the all‑VoIP networks operators want for optimal integration of voice and data services possible. Doing so would allow operators to provide high data-rate services to handsets in the same way that wireline operators provide such services to homes today. At the same time, they could also provide the greater efficiency required for voice services. 

Figure 1: The industry and technology current situation

Another key feature of LTE is its potential to deliver sufficient bandwidth to support video services to individual users. Channel bandwidths from 1.25 to 20 MHz are supported in the standard, with ultimate performance requiring a 20-MHz spectrum allocation, and providing a headline cell data rate of 100 Mbps. Support for the higher speed channel and increased transmission reliability – both of which are needed to reach LTE’s low-latency target – comes from the new OFDM-based (Orthogonal Frequency Division Multiple Access) air interface and MIMO (Multiple Input Multiple Output) diversity.

Challenges Ahead

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 2 years ahead of any service introduction. This will ensure user devices are available in volume when the network services are finally launched. At the same time though, this timescale challenges everyone in the food chain including component suppliers, users, network equipment developers, and of course, test equipment companies like Agilent Technologies who must support the standards with new measurement capabilities throughout the product lifecycle - from early R&D through to volume manufacturing.  

As with HSPA, user-equipment chipsets are being designed to have as long a life as possible, so that manufacturers can recover their massive investment costs over a longer period. This means the headline rate supported by a chipset will be much greater than the data rate that will be available to the device in a network.  However, vendors will want to confirm correct operation up to the maximum rate that the chipset is designed to support. Consequently, test instrumentation needs to be capable of supporting higher rates and channel bandwidths early in the design cycle. With HSDPA, for example, this means that test equipment needs to support at least 7.2 Mbps today, although networks are set up to deliver a maximum of 1 Mbps to an individual handset.

Another measurement challenge lies in the changing block diagram of both network and user equipment. New generations of base station radios rely more heavily on "software radio" architectures, which allow operators greater flexibility to upgrade their capabilities. Now, standards such as DigRF are moving handset design along similar lines. Such systems use greater integration of digital and RF into single devices to eliminate or hide traditional test interfaces. They also make use of software correction in the digital domain to achieve desired RF performance. With the addition of MIMO, data from independent transmit and receive channels is combined to maximize correct reception. These changes require new measurement processes and equipment to allow the correlation of digital and RF data. 

With its flexible platforms, Agilent is a prime example of a test equipment company that is committed to supporting early R&D. More importantly, it is committed to tuning those platforms to support the specific needs of LTE test as user requirements become clear. For measurements that cross the digital-to-RF divide, Agilent provides solutions which range from individual RF and logic analysis products to complete system simulation via Agilent eeSOF products. It also boasts the ability to connect these products together to combine real‑world measurements with simulation data. And, for today’s network operators, Agilent provides solutions from protocol analysis tools for interoperability troubleshooting to drive test products that help optimize and find network coverage holes. It also offers QoS monitoring systems to help ensure the availability of data to measure user experience.