Wireless cellular systems are moving from narrowband 2G Global Systems for Mobile Communications (GSM), IS-95 systems to Wideband Code Division Multiple Access (W-CDMA)-based 3G and 3.5G systems.
As these standards progress, wireless base station OEMs must gear up with newer, better, more powerful, yet cost-effective technologies to handle the increasingly higher data rates these systems demand.
In the near future, third-generation partnership project long-term evolution (3GPP LTE) specifications will require complex signal processing techniques such as multiple-input, multiple-output (MIMO) along with new radio technologies like orthogonal frequency-division multiple access (OFDMA) and multi-carrier Code Division Multiple Access (MC-CDMA).
With technology demands like these looming in the near term, mobile and wireless service providers and operators want wireless base station OEMs to assure them the base stations they're placing in the field have the capability of supporting LTE.
Operators are adamant about avoiding "rip and replace" situations. This means OEMs need to "future proof" their base stations with multi-protocol designs.
A multi-protocol base station is defined as one that can support W-CDMA to LTE standards. A base station family of this caliber will require the capability to move virtually seamlessly from one 3GPP release, for example, to a newer one in the same family without major costly re-designs.
Hybrid FPGA/digital signal processor-based platforms provide an effective design approach to comply with these ever-changing wireless standards. Intelligent partitioning between the FPGA and digital signal processor must be based on system throughput requirements and long-term cost considerations for product success. As standards stabilize, initial requirements for base station design flexibility should subside, while cost becomes a major success factor.
Selecting FPGAs with a risk-free migration path to low-cost structured ASIC technology translates into significant cost savings. For instance, Altera's HardCopy II technology provides a seamless, risk free migration from Stratix III FPGAs to significantly lower cost HardCopy II structured ASICs, while also increasing system performance and decreasing power consumption.
Evolving designs
Wireless operators worldwide are currently using High Speed Downlink Packet Access (HSDPA), which follows successful deployment of Universal Mobile Telecommunications Systems (UMTS) networks. The UMTS to HSPDA upgrade is similar to Enhanced Data Rates for GSM Evolution (EDGE), which has proven to be an effective upgrade to GSM networks.
HSDPA is targeted at mobile multimedia and can achieve reduced delays and peak data rates up to 14 megabits per second (Mbps) in the downlink from base station to mobile terminal. This is made possible by the addition of a new high-speed downlink shared channel along with three fundamental technologies relying on rapid adaptation of transmission parameters to the instantaneous channel conditions. Those are adaptive modulation and coding (AMC), fast hybrid automatic-repeat-request (ARQ) and fast scheduling.
High Speed Uplink Packet Access (HSUPA) will soon follow HSDPA, and the combination of the two technologies is called High Speed Packet Access (HSPA). HSPA is expected to be the dominant mobile data technology for the rest of the decade. To leverage operators' investments in HSPA, standards bodies are examining a series of enhancements to create "HSPA Evolution" also referred to as "HSPA+."
HSPA Evolution, a logical development of W-CDMA, provides an effective transition to the completely new 3GPP LTE radio platform. LTE uses OFDM on the downlink and is targeted for deployment around 2009.
LTE taps the best-of-breed radio techniques to reach performance levels beyond what is practical with CDMA approaches. LTE systems will co-exist with 2G and 3G systems similarly to the way 3G co-exists with 2G systems in integrated networks.
Meanwhile, OFDM communications system designs continue making greater inroads. OFDM is a multi-carrier modulation scheme that encodes data onto a radio frequency (RF) signal.
