All About Cellular TX-CEL

New technique to improve Cellular modem data through-put

The Problem

Prior to the introduction of Throughput X-Cellerator (TX-CEL), transmitting data over cellular systems was slow, unreliable, and costly. Modems without TX-CEL spectral shaping have difficulty connecting reliably at speeds above 4800bps over cellular channels, and those that do connect, have trouble faxing or maintaining connections during large file transfers.

Until recently, the modem industry viewed the cellular environment as hostile to data, and therefore used sophisticated error correction protocols that make connectivity possible, but also adds significant overhead due to numerous re-transmissions caused by link layer errors. These re-transmissions severely limit modem performance. As such, transmitting data and fax without TX-CEL over cellular systems is not considered a viable wireless communications option.


The Solution

Rather than develop a competing error correction protocol, Celeritas decided to address the cellular network impairments in an attempt to reduce the number of physical layer errors, and the corresponding re-transmissions they cause, thus improving overall cellular data and fax transmission performance. The result was TX-CEL, a patented state-of-the-art cellular modem firmware technology that improves modem performance independent of the error correction protocol used.

TX-CEL utilizes filtering techniques to reshape the analog data waveform transmitted by a cellular radio connected to a computing device. Celeritas has discovered that noise reduction processes used to enhance voice quality in cellular transmitters (cellular phones and cell sites) will distort high frequency elements of data signals sent by modems. TX-CEL changes the shape (spectral content) of the data waveform transmitted by cellular modems so that high frequency elements avoid this distortion. Therefore, cellular modems with TX-CEL technology are able to communicate reliably at high speeds with performance similar to that available when connected to standard wall phone jack. In addition, since TX-CEL firmware eliminates errors, the importance of cellular error correction protocols is significatly reduced.

With modems using TX-CEL firmware, more air time is dedicated to cellular data transmission since the number of re-transmissions caused by physical layer errors is dramatically reduced. TX-CEL firmware ensures significantly higher connectivity, data throughput, and reliability. Independent test result summaries with TX-CEL in the send and receive modems include the following performances:



Higher connect rates; 14,400 bps or faster


Increased data throughput. Without compression, throughput is consistent at the modem modulation rate. With compression, throughput approaches the maximum Data Terminal Equipment (DTE) rate, generally 57,600 bps.


Dramatically improved reliability, especially while moving and in fringe areas.

Copyright (C) 1995, Celeritas Technologies, Ltd.

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