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AN ECONOMICAL IMPLEMENTATION OF ACCURATE AND REPEATABLE RSSI IN A WIRELESS SYSTEM

IP.com Disclosure Number: IPCOM000009526D
Original Publication Date: 1999-Sep-01
Included in the Prior Art Database: 2002-Aug-29
Document File: 3 page(s) / 146K

Publishing Venue

Motorola

Related People

Michele Clayton: AUTHOR [+4]

Abstract

The accuracy, repeatability and resolution of the received signal strength (RSSI) in a network sub- scriber unit are very dependent upon the characteris- tics of the individual hardware components. Due to variation in parts, the accuracy of RSSI measure- ments in a network subscriber unit has always been less than that needed to detect subtle changes in RF performance. In addition, the network subscriber unit does not measure RSSI to a tine resolution and the repeatability of readings is less than desirable for some applications. Network subscriber units also lack the ability to provide accurate RSSI readings over a wide range of temperatures without a great deal of cost. Typically, accurate RSSI readings are implemented with complex circuits consisting of many hardware devices. Hardware of this type is costly to build due to the number of circuits that need to be tuned. The circuit method of implementa- tion also requires that the hardware parts produce linear or nearly linear RSSI. If the hardware is not linear, then the control and measurement software is very complex and typically involves at least a sec- ond order correction or interpolation algorithm.

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Developments Technical 0 M MO7VROLA

AN ECONOMICAL IMPLEMENTATION OF ACCURATE AND REPEATABLE RSSI IN A WIRELESS SYSTEM

by Michele Clayton, Art Helwig, John Tunny and Joe Walsh

  The accuracy, repeatability and resolution of the received signal strength (RSSI) in a network sub- scriber unit are very dependent upon the characteris- tics of the individual hardware components. Due to variation in parts, the accuracy of RSSI measure- ments in a network subscriber unit has always been less than that needed to detect subtle changes in RF performance. In addition, the network subscriber unit does not measure RSSI to a tine resolution and the repeatability of readings is less than desirable for some applications. Network subscriber units also lack the ability to provide accurate RSSI readings over a wide range of temperatures without a great deal of cost. Typically, accurate RSSI readings are implemented with complex circuits consisting of many hardware devices. Hardware of this type is costly to build due to the number of circuits that need to be tuned. The circuit method of implementa- tion also requires that the hardware parts produce linear or nearly linear RSSI. If the hardware is not linear, then the control and measurement software is very complex and typically involves at least a sec- ond order correction or interpolation algorithm.

  The solution presented here provides the follow- ing improvements for wideband RSSI at a very low cost:

  1. Any receiver can now guarantee the accuracy and repeatability of measurements for received sig- nal strength regardless of application, waveform and differences in individual RF or digital hardware components. Data confiis that the RSSI circuit and algorithms perform at a high level of accuracy and repeatability. At room temperature, the typical worst-case RSSI measurement is *ldB or less from actual input over all power levels and frequencies. At an external temperature of 65"C, the typical worst-case RSSI measurement is i1.5dB or less from actual input level over all power levels and fre- quencies. The worst case includes measurements taken at the edges of the hardware's measurement capability.

  2. Using these algorithms, RSSI accuracy and repeatability are guaranteed over a wide range of temperatures. The ability of the hardware to detect a RF signal is the only limit to the range of input power. For a CDMA application in which this method has already been implemented, the guaran- teed range of input power is from -25dBm to -95dBm. The CDMA product guarantees accuracy and repeatability for a temperature range of external temperatures between -15" to (65°C or an internal temperature of 0°C to +8O"C. Both the temperature and power ranges can be greatly expanded from that which has been guaranteed in the CDMA product

   3. The number of hardware components need- ed to implement this method is greatly reduced as compared to traditional methods, thus reducing the cost. The need for perfect linearity in hard...