POTS
 

Wireless remotes are an ongoing challenge, but Comrex continue working on new and improved methods to overcome the current limitations of mobile technology. At the same time, mobile networks continue to progress toward third-generation wireless (3G) and the increased bandwidth will allow remotes to be more dependable and at higher sound quality. Today, the Comrex Matrix and BlueBox can be used on GSM networks; while wireless networks typically yield lower sound quality than POTS/PSTN connections, the codec significantly improves the sound over that of a handset wireless call.

A BRIEF HISTORY OF WIRELESS TELEPHONES

The first generation of U.S. cellular telephone service was first available in the early 1980s. This analog system, Advanced Mobile Phone Service (AMPS), operated in the 800 MHz band. Europe, however, had a number of incompatible wireless technologies across the continent, until 1983, when the Groupe Speciale Mobile developed a digital standard (GSM: Global System for Mobile Communications) to use throughout Europe.

In the United States, a frequency range in the 1900 MHz band was auctioned in 1993 to become the home for Personal Communications Service (PCS), a digital technology allowing phones to send and receive data, not just audio. PCS today encompasses three individual technologies:

1. Time Division Multiple Access (TDMA): TDMA is often deployed by companies who have a large, existing analog network (due to lower deployment costs) and is being phased out due to its lack of high-speed data capability.

2. Code Division Multiple Access (CDMA): CDMA is technically quite different from the other two protocols. CDMA is used by Sprint PCS and other regional carriers, including US West Wireless; it is also being deployed in Asia.
    

3. Global System for Mobile Communications (GSM): This system, developed in Europe, has become the predominant wireless telephone technology outside North America. In the U.S., GSM trails in use to TDMA and CDMA; U.S. carriers include T-Mobile and Cingular.

CODECS AND WIRELESS

While CDMA supports the fastest speeds of the three protocols (14.4kb/s), the data stream is excessively bursty, so the resulting congestion may cause some portions of your data to be delayed significantly. Without reliably constant throughput, CDMA is not a feasible option for real-time audio.

GSM, then, is the only suitable network for real-time audio. Despite the relatively low bandwidth (7.8 or 9.6 kb/s), our testing shows success on GSM networks. The new Vortex Matrix and BlueBox codecs are equipped for operation on all GSM networks, providing about 5kHz audio response.

USING THE CODECS ON WIRELESS

Today's Matrix and BlueBox units have two modes of wireless use:

1. Cellular Hands-free - Microphones and headphones may be interfaced with the "Hands-free port" on a variety of cell phones by using the optional TelCell module on the Matrix or the "Cell Phone Jack" on the BlueBox. While this method is still limited to the phone's frequency response, professional microphones will typically lead to an audible improvement over the cheap ones found in most mobile phones. For most Motorola phones, you will need a 1/8"-to-2.5mm cable, available from Vortex. The hands-free port on other brands may be adapted for use with the BlueBox or Matrix TelCell module. For more information, you can read:
    

2. Data - Select GSM mobile phones can be connected to the 9-pin multipurpose port on the Matrix or BlueBox to achieve up to 5kHz of frequency response. The remote and studio codecs must both be configured for wireless use. For this use, you will need an external mobile phone, a data cable, and a null modem adapter (available from Vortex for no charge).

COMING SOON FROM Comrex

Comrex has even more in the works. Coming soon, a new upgrade for the BlueBox and Matrix will use a new algorithm that improves frequency response (up to 7kHz) while reducing the audible artifacts. Previous units will be upgradeable.

Also, the new portable GSM module for the Matrix portable will make GSM connections dramatically easier. The module contains a GSM phone, set to North American or International GSM frequencies, eliminating the need for an outboard phone. Equipped with an external antenna and a 2-watt power booster for higher power than handheld phones, the module will improve reception, and the software will allow for minimized network delay times. For instances where a codec connection is impossible, the module allows the portable Matrix to act as a hybrid on your GSM network and make ordinary voice calls.

WIRELESS IN EUROPE

European wireless providers have made headway toward high-speed service, beginning to implement High Speed Circuit Switched Data (HSCSD), which allows higher data rates on GSM by using two telephone channels to transfer frequency response as high as 10-12kHz. We currently recommend the Nokia 6310 phone for this use.

WIRELESS IN THE FUTURE

Wireless is moving toward the so-called 3G, the third generation of wireless technology, following analog and PCS. Meanwhile, a number of interim "2.5G" solutions have arisen, services including GPRS, 1XRTT, and EDGE. Some PCS providers are upgrading to these standards, which can provide upward of 100kb/s, without the need of a complete redesign. We are not supporting codecs on these services for several reasons:

1. Data throughput is typically asymmetrical on these services, allowing only a low speed from the wireless phone to the network - the direction high speed is needed for our applications.

2. Rather than dial-up services, these are connections to the Internet, similar to an ISP and subject to the congestion and burstiness associated with the public Internet.

3. These services are "best effort," meaning that if someone makes a voice call within your cell site, your data rate can be throttled down.

3G will offer rates of 384kb/s up to 2Mb/s in a stationary environment, supporting wide-bandwidth needs, such as full-motion video. While the bandwidth will remain Internet protocol-based and subject to congestion, design for multimedia and wide bandwidth will help reduce today's limitations. Early 3G networks have already begun to spring up: in Japan, NTT DoCoMo launched its 3G "FOMA" service in October 2001, and European networks are in development. Implementation in North America should be introduced in the upcoming years.

Be sure to check back for updated information on this ever-changing technology

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