>> CDMA Cell Phone DTMF Shortfall
Xtel is presently working upon an upgrade to make the XTA callout unit compatible with the Telus Mobility CDMA digital cell phone network.
Background: Telus is slowly transitioning all of the cellular network to CDMA (code division multiple access) digital from the analog AMPs (advanced mobile phone service). The CDMA network is based on a spread spectrum chipset developed by QUALCOMM Incorporated of San Diego USA. This chipset performs compression on the users audio signal to reduce bandwidth and allow the network provider to support more traffic on less bandwidth. This compression is what delays, distorts and generally reduces the quality of your voice when you use the CDMA network. Unfortunately, when Qualcomm designed the chipset they only supported TouchTone (DTMF) send from the mobile terminal. TouchTone (DTMF) receive, modem tones, or any other signaling tone from the network to the mobile device was not envisioned. This is why you cannot directly use dial-up modems on the CDMA cell phone network. TouchTone (DTMF) is distorted by the CDMA voice compression making it difficult to decode with standard DTMF tone detectors.
Present Situation: Telus has standardized on a number of Wireless Land Line CDMA cell phone products that provide a telephone interface to XTA callout units (Phonecell® SX4T CDMA2000 1X Fixed Cellular Terminal and Phonecell® SX5T-500C / SX5T-505C Fixed Cellular Terminal). These products will provide the user with reliable callout. However, the user will experience difficulty using TouchTone (DTMF) to enter commands to the XTA. The zero and star keys are especially difficult to decode from the CDMA cell phone.
Telus’s CDMA cell phone offerings are workable with an XTA, IF the XTA user sets the XTA password to non-zero digits and limits usage to acknowledging alarms.
Xtel Developments: Xtel will be announcing an upgrade to the XTA product line that will provide inexpensive and reliable TouchTone (DTMF) receive using CDMA cell phones.
TouchTone - Bell Systems