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For example, there is a choice among different modulation schemes, such as FSK, GFSK, ASK, and OOK. Requiring few external components and offering a high degree of flexibility, it allows the user to configure the part for specific applications. It is capable of operating in the 433 MHz and 868 MHz European ISM bands (ETSI EN300 220-1 standard), and the North American 902 to 928 MHz band - covered by FCC Part 15 regulations. The ADF7020 is a complete monolithic radio transceiver built using 0,25 μm CMOS technology.
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The two main chips share the same power supply voltage (2,3 V < V CC<3,6 V), and they are directly connected for 'control' operations, using the ADSP-BF531 flags (digital I/Os) and 'transmit/receive' operations, using one of the serial synchronous ports (SPORT0).ĭata will be transmitted to - or received from - the modem, either asynchronously over the UART or synchronously with the remaining SPORT. Thanks to its 400 MIPS (million instruction-per-second) and 800 MMACS (million multiply-accumulate-per-second) capabilities, the ADSP-BF531 can also accommodate protocols to support various wireless configurations and topologies, including point-to-point, multipoint, and broadcast, as well as sophisticated encryption and source coding and decoding algorithms such as Motion JPEG (MJPEG).įigure 1 is a detailed circuit diagram of a wireless digital modem built around the ADF7020 ISM-band transceiver and its companion controller, the ADSP-BF531. When used in conjunction with the ADF7020 ISM-band transceiver IC, with its typical range of several hundred meters (line of sight), this approach provides a robust solution for designers wanting to replace their current wire-line solutions without compromising quality of service. A low-cost, yet powerful, processor such as the Blackfin ADSP-BF531 can be used to implement intensive error-correction techniques requiring millions of instructions per second (MIPS) - convolutional coding with bit-scrambling and interleaving, for example - to deliver a data rate of over 100 kbps with a transmission error rate of less than 10 -6. Such longer associated transmission times also increase the overall system power consumption.Ī powerful solution to this dilemma lies in the use of forward error-correction (FEC) techniques, able to detect and correct errors over a large enough number of bits to compensate for partial packet loss and ensure service quality. It also introduces problems in industrial process-control and telemetry systems, which must maintain throughput in a noisy environment without the need for many retransmissions. But it does become a problem for applications such as wireless audio or video transmission, with their higher data rates, since the latency introduced by ARQ might be unacceptable. This need to retransmit corrupted packets is not particularly onerous for a low-throughput system - one that sends a burst of data from a remote sensor once every few minutes, for example. CRC can detect this corruption to a certain extent and trigger the retransmission of erroneous packets (this is usually called automatic repeat request, ARQ), but at the cost of considerable delay and loss of performance in realtime applications. A traditional way of dealing with this problem is to use some sort of error-detection technique, eg, cyclic redundancy checking (CRC). In wireless systems, data will be corrupted if an interferer collides with the wanted signal - resulting in an insufficient signal-to-noise ratio (SNR) at the receiver. As might be expected, there are plenty of legacy systems already operating in these bands. Unfortunately, one cannot entirely eliminate the problem of interference and co-existence by simply switching to these lower-UHF bands. However, this burden has been eased considerably by the introduction of flexible ISM-band transceivers, such as the ADF7020, which allow operation from 433 MHz to 960 MHz. Unlike at 2,4 GHz, however, there is no common global standard for the lower-UHF bands this means that a manufacturer's system would have to be adaptable to each region's regulations.
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Because of the heavy traffic in the 2,4 GHz band, and its associated co-existence issues, interest has increased in the ISM (industrial, scientific, medical) UHF bands - available at the lower frequencies of 868 MHz and 433 MHz in Europe, and 902 MHz to 928 MHz in the United States. Most of these applications - Bluetooth, WLAN 802.11b, and cordless telephones, for example - are appearing alongside the microwave oven in the license-free UHF band at 2,4 GHz. In the last few years, radio-frequency technology has advanced by leaps and bounds, resulting in a phenomenal number of new wireless applications. Patrick Butler and Austin Harney, Analog Devices