Edge technologies keep up with demand

The Edge technology has matured in terms of worldwide coverage, stable infrastructure and the variety of handsets supporting its features. Low-cost infrastructure upgrades and the availability of Edge features in most mid- to high-end handsets provide a compelling price-performance argument for Edge deployment.

This technology has brought key innovations to the radio link, including the introduction of higher-level modulation (8-PSK); multiple coding-modulation schemes MCS 1-9, which allow systems to adjust to operating conditions; and incremental redundancy, which provides link gains by combining different transmitted data. Edge offers increased data rates with a theoretical peak rate of 473.6Kbps and is effective in expanding data capacity with an average gain of over 3x compared with GPRS.

Edge goes beyond improvements in radio performance. It supports the same QoS architecture used by UMTS, which allows the evolution of services offered through future 3G Partnership Project (3GPP) releases.

While Edge provides significant improvements over existing GSM/GPRS networks, it can also coexist with other radio-access technologies, such as UMTS and 3GPP LTE. The next important factor contributing to Edge's success is the introduction of wireless data services. Higher data rates offered by Edge coincided with user demand for wireless e-mail, content downloads, Internet Protocol multimedia subsystem and enterprise applications.

New capabilities
Evolved Edge emerges as an attractive technology for operators, as it offers efficiency comparable to 3G systems while relying on existing spectrum licenses.

Edge technology presents many challenges to wireless handset platforms. On one side, the complexity of new standards points to ever-increasing computational and memory requirements. On the other, commercial pressures demand that higher capability be offered at competitive power-consumption levels and cost with respect to mature technologies such as GSM/GPRS. The answer to these challenges, which are far from unique, relies on the availability of fundamental technologies and the creativity of design teams. The optimization of the handset platform considers these factors: advanced IC manufacturing process; multicore digital baseband architectures; increased levels of integration ranging from core/memory to mixed-signal and RF on a single chip; multichip packaging technologies; software optimization techniques for reducing power consumption; and software-reconfigurable platform for flexible handset design.

Edge has introduced the clear dividing line for "sub-100MHz" processors, which failed to fulfill the requirements of the PHY layer and required specialized hardware accelerators or a coprocessor.

Unlike GPRS, the complexity of Edge is that there is no de facto data-receiver solution—algorithms that are adopted in chipset realizations range from the family of sub-optimal trellis-search-based solutions to more computationally-demanding techniques. Depending on HW/SW partitioning, some or all computations can be offloaded to a hardware block. The trade-off typically goes toward preserving key parameter computations and prefiltering in software. In addition, critical performance figures of the data receiver are a function of synchronization capability and filtering techniques for interference suppression, which are coupled with receiver design.

Edge advantage
With DSPs intended for cellular baseband processors reaching speeds well above 200MHz, the Edge data receiver can be implemented completely in software. It is flexible enough to adapt to changes in the standard as well as to changes required to implement extensive field test cases and secure operator approvals. This can be achieved by a low-power core design, which allows the overall power profile to equal or even surpass that of GPRS digital baseband chipsets while maintaining a high degree of flexibility.

A software Edge implementation has the advantage of a handset hardware design, which remains stable while performance is optimized in the type of approval and interoperability test process used on multiple vendors' infrastructure. The cost-effective and power-efficient solution meets stringent wireless handset requirements. Moreover, a software-based, future-proof platform allows for the addition of performance-enhancing techniques, ranging from proprietary algorithms for enhancing Edge to incorporating other advanced processing techniques such as single-antenna interference cancellation or elements of Evolved Edge.

Looking further into the handset's functions, there is an increased requirement for high-level applications. In this domain, the capability is based on the resources of the MCU core. Typically, solutions based on the ARM7 core present a highly optimized communications platform suitable for data cards and entry-level handsets. However, they require significant hardware support for multimedia functions, or dedicated DSP core or hardware acceleration for audio/video.

The next level of multimedia capability is introduced with the combination of the more powerful ARM9 core and an enhanced DSP core.

A typical multicore solution has a DSP subsystem, which consists of the DSP core, L1 code and data memories (configurable as cache or SRAM), unified L2 memory and a set of DSP peripherals.

A typical multicore solution has a DSP subsystem, which consists of the DSP core, L1 code and data memories (configurable as cache or SRAM), unified L2 memory and a set of DSP peripherals. The DSP subsystem handles the channel equalization, data receiver and voice codec functions.

The MCU subsystem consists of the MCU core and cache. The ARM cores available from Advanced RISC Machines are almost universally used for the MCU block. Multimedia interfaces for display and image-capture devices can be supported by the dedicated bus subsystem. It may include a parallel peripheral interface controller, supporting a multibit camera sensor or video input interface and a dedicated external bus interface for parallel LCDs. The data-movement needs of the multimedia interface devices could be supported by the multichannel DMA controller, which supports necessary video formats.

The elements of a typical Edge handset chipset include the RF transmit/receive portion, analog baseband with mixed-signal and power-management blocks, and digital baseband. A complete phone design includes the chipset, memory modules, applications modules and peripherals (e.g. Bluetooth, secure digital card or MMC).

A complete Edge phone design includes the chipset, memory modules, applications modules and peripherals, such as Bluetooth, or a secure digital card or MMC.

The chipset in the figure is based on a proven and stable platform approach with a cost-effect partitioning in today's process and package technology. This platform is extremely competitive in terms of active and standby power, which has been achieved by integration of power management and architectural choices on digital baseband. This architectural approach allows for seamless migration to an increased level of integration, using either a system-in-package or SoC that will inevitably come with the move to the next process node (i.e. 65nm).

The platform's scalability makes it possible to extend the architecture to multimode operation. It can also achieve the necessary speed for many user requirements, provide scalable power consumption, efficiently handle control code and support the optimizing of the compiler for production code quality. In addition, it directly benefits from the years of investment in performance/cost improvement and power reduction in GSM, GPRS and Edge. This includes the use of dynamic voltage scaling to match power consumption with processor performance, and the use of such advanced RF and mixed-signal techniques as direct conversion receivers and ΣΔ data converters.

-Zoran Zvonar
Manager, Systems Engineering Group
Analog Devices Inc.