Expanding Capacity

Are you scrambling for RF breathing room? Regardless of technology choice and location, whether metropolitan or rural, most service providers are supporting saturated networks and face increased demand. You need fast, effective and cost-efficient ways to add wireless capacity.

A new generation of CDMA, GSM and TDMA base-station solutions -- supported by a toolkit of software and strategies -- can allow you to deploy affordable and highly flexible capacity where and when you need it most. This capacity-oriented approach is changing the way many providers plan and manage growing networks.

CDMAExperts project there will be 45 million CDMA customers by 2000. With four to seven operators competing for most U.S. markets, commodity pricing is driving down revenue-per-subscriber performance. Factor in high distribution costs and increasing churn rates, and it is difficult to hold the bottom line. But savvy operators are finding ways to pack more capacity into existing CDMA network investments.

No single BTS can meet every infrastructure requirement. But by balancing coverage and capacity needs -- and by applying flexible new platforms and refined traffic-management techniques -- you can optimize capacity solutions for a range of market situations.

The best of these new platforms are highly modular solutions that support cdmaOne (IS-95 CDMA) at 800MHz and 1.9GHz, while supporting a smooth evolution path to future standards. Advanced BTSs deliver exceptional capacity performance and flexibility. A typical outdoor configuration, for example, provides from one to three carriers of digital electronics in a single tri-sector enclosure.

By employing fiber to connect the digital enclosure to the radio enclosure, new base stations eliminate signal loss, thus reducing installation costs for indoor and outdoor configurations and conserving bandwidth for future requirements. The power systems and power-efficient designs in new metropolitan cells use up to 40% less power than current base stations. ATM-based network architectures further reduce networking and implementation costs and support the high-bandwidth IP applications of the future.

High-capacity base stations provide flexible sectorization schemes using up to six available sectors. Future software releases are expected to support up to nine sectors. Current indoor applications support the initial tri-sector carrier in a single frame, with modular upgrades available for second-, third- and fourth-carrier functionality installed in a second RF-only frame.

This highly flexible approach allows you to mix and match capabilities to meet the deployment requirements of fixed applications, hybrid wireline/wireless, fixed/mobile wireless situations and high/low density applications. You can enjoy maximum-capacity efficiencies while getting more coverage from a smaller equipment footprint.

The evolution of CDMA technology standards also extracts the most capacity possible from your network investment. The original IS-95 Rate Set 1, 8K vocoder has evolved to the current Rate Set 2, 13kb/s vocoder. Today's latest platforms support the enhanced variable rate codec (EVRC), an IS-127 standard enhanced 8kb/s vocoder, which offers a 30% capacity increase.

A standard under development, CDMA2000 1XRTT, is expected to double capacity. This increase in spectral efficiency will provide significant RF capacity improvements for a relatively small investment.

You also can expand CDMA capacity through new platforms that support the evolution to high-capacity multicarrier architectures. Multicarrier CDMA technology offers a flexible and affordable capacity solution for high-density 800MHz and 1.9GHz wireless networks as well as for low-density markets.

Today's most advanced CDMA platforms provide scaleable capacity, and you can configure them to start with a single carrier or frequency in an omni-sector environment. You then can convert them quickly and easily to provide multiple-sector and multiple-carrier performance.

Multicarrier platforms consist of an RF cabinet containing the radio hardware and a digital enclosure containing the channel element cards used to process calls in the multicarrier configuration. When you assess multi-carrier equipment, you should look for platform equipment that is modular, fiber- and ATM-based, and that provides both backward-compatibility and a smooth pathway to 3G standards.

Currently, there are two main CDMA multicarrier network approaches. Each uses a unique strategy to assign calls among available frequencies.

One multicarrier approach assigns calls based on the originating call's MIN, essentially using a simple even/odd strategy to allocate call traffic among available carriers. This method, called hash multicarrier traffic allocation, is less efficient because it relies on the statistical assumption that networks experience even- and odd-numbered MINs in roughly equivalent and simultaneous volumes.

The second, more advanced approach to multicarrier call allocation uses highly evolved software to optimize all available frequencies. Software constantly assesses the CDMA network's dynamic traffic environment and, when a call is originated, automatically assigns it to the frequency offering the greatest available capacity. This method pools voice resources in a common trunk group and increases Erlang capacity. As a result, overloaded networks and dropped calls are less likely.

In a multicarrier infrastructure, you can add carriers as needed to meet the RF-capacity requirements of dense suburban and urban sites, most often in a classic "wedding cake" configuration. Some metropolitan operators build additional multicarrier capacity into their networks so that as subscriber demand grows, they can add carrier capacity quickly and economically.

This multicarrier approach delivers greater coverage, easy maintenance and a smooth pathway to system upgrades. A multicarrier configuration also allows you to shift network resources to meet market demands.

GSMNorth American GSM carriers have built more than 8,500 cell sites in less than three years. GSM is one of the fastest growing technologies, with forecasts of more than 200 million worldwide subscribers by 2000.

To satisfy this robust demand, GSM providers are deploying capacity-oriented base stations that provide exceptional RF performance, improved transmission capabilities and highly optimized modular packaging.

New GSM base stations provide guaranteed dynamic receiver sensitivity of -110dBm and advanced interference cancellation algorithms to deliver broader coverage and improved voice quality by incorporating EVRC technology, while reducing site-count and network cost requirements. Advanced hand-over algorithms and frequency-reuse engineering techniques offer the best balance between quality of service and network capacity.

Next-generation GSM solutions can go from a simple omni-directional base station with a single GSM radio to a tri-sector base station with eight radios per sector in three cabinets. They offer new features including frequency hopping in synthesized and base-band modes, microcellular handoff algorithms, increased static and dynamic power control, and improved availability based on the duplication of common functions and optional N+1 transmission function redundancy.

You also can manage growth through an innovative technique designed to maximize spectral efficiency. The fractional frequency-reuse technique allows you to increase network capacity by more than 100%, improve end-user voice quality and at the same time eliminate the need for costly new cell sites. This method employs smaller reuse patterns, advanced GSM features and fractional loading techniques to optimize frequency efficiency.

One-by-three or 1x1 reuse patterns are used for non-broadcast control channel (BCCH) transceivers (TRXs), with the TRXs broadcasting the BCCH channels continuing to use conventional 4x12 reuse patterns to provide mobiles with the needed reference signals. This approach requires advanced GSM features to offset co-channel interference. Fractional loading principles also give you the flexibility to engineer more productive and less costly networks.

GSM operators also are responding to network-capacity challenges by deploying micro-cellular base stations and by integrating dual-band base stations, engineering tools and interband traffic management features.

TDMATDMA systems are deployed in 70 countries around the world. With predictions that TDMA subscribers will surpass 42 million by 2002, operators are optimizing networks and planning for the future. In crowded urban environments, TDMA carriers need to deploy a new generation of dual-mode base-station solutions that deliver maximum flexibility and higher capacity.

Advanced platforms support TDMA traffic as well as AMPS CDPD, using refined dual-mode radio transmit/receive components. Featuring compact footprints and high capacity, these TDMA cell sites deliver high channel counts at low costs for low-to-medium power applications. Configurable as omni-, bi- or tri-sectored with up to 120 radios per cell site in multiple sectors, these cell sites are highly versatile.

The high-capacity, dual-mode cell sites employ innovative multichannel power amplification (MCPA) technology to deliver flexible power outputs. The advanced MCPA approach allows tighter channel spacing, operating with as little as 5-channel spacing without reducing output power. This supports high-frequency reuse and enables a smooth migration path from the typical N=7 reuse pattern to the higher-capacity N=4 pattern.

The new generation of TDMA cell-site systems provides reliable soft-fail capabilities, which prevent capacity loss during amplifier failures. Amplifier hot-swaps simplify maintenance and reduce costly network downtime. An automatic power-control system provides overdrive protection for the amplifier and maintains intermodulation performance.

To extend the TDMA network approach, you also can add a new generation of low-power indoor platforms. Ideally suited for public and private network applications, these compact base stations provide affordable and easy-to-deploy solutions for malls, offices, hotels, campuses and other hybrid applications.

By combining the advanced capacity-oriented features of new cell-site systems with a growing range of RF-capacity software tools, you can squeeze even more capacity from your TDMA network investments.

For example, the frequency-reuse strategy groups usable cellular frequencies into clusters of cell sites, allowing you to reuse frequencies with minimal adjacent or co-channel interference. The goal of frequency reuse is to balance RF capacity and the carrier-to-interference (C/I) ratio, while optimizing network capacity and quality.

In many TDMA applications, a 3-sector, N=7 frequency-reuse plan, which yields 416 channels for A and B cellular bands, is suitable for balancing capacity and audio quality. However, as capacity requirements increase, you may want to implement the advanced N=4 frequency-reuse plan.

As the frequency-reuse plan becomes more aggressive, the likelihood of adjacent and co-channel interference also increases. When implementing an N=4 frequency- reuse plan, you can deploy advanced RF software features that decrease adjacent and co-channel interference, improve network audio quality and provide an improved C/I ratio. These features include adaptive cell tiering, adaptive channel allocation and hierarchical cell structures.

Adaptive cell tiering reduces system interference and dropped calls by dynamically assigning channels to an inner or outer tier where power levels define tier boundaries. Adaptive channel allocation assigns dynamic radio queues to any available voice channel, automating up to 50% of frequency assignments and delivering 30% capacity gains.

Hierarchical cell structures feature low-powered cells overlaid by higher-powered macrocells. In a hierarchical configuration, the macrocell typically serves large areas with diverse user populations, while the smaller hierarchical cells are used to cover specific high-use areas.

The industry's most recent generation of capacity-optimizing software provides even more capabilities. By more precisely managing power requirements, bit-error-rate-driven, mobile, base-station power control reduces system interference, improves audio quality and dramatically increases available RF capacity. Other capacity-enhancing strategies include mobile-assisted channel allocation and adaptive handoff reserve.

Growth will continue to be a key market driver in most markets for years to come. Manufacturers serving CDMA, GSM and TDMA are unveiling a powerful new generation of capacity-driven solutions. By deploying capacity-oriented base-station solutions and by leveraging the power of advanced software and frequency use strategies, your networks will be able to grow with your subscriber base.