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Wireless HD Video Product Information

Silvus attacks from multiple technological approaches

Applications that demand higher data rates, such as HDTV (720p up to 1080i) and streaming video, require wireless data throughput rates of 100M bit/sec and higher. Achieving this throughput within the unlicensed band requires improvements in the physical layer (that is, the raw data rate) and the efficiency of the media access control (MAC) layer, such that the throughput is closer to the raw data rate. Throughput in excess of 100M bit/sec in 20MHz to 40MHz of bandwidth that will be operational in a real world environment is a very challenging engineering task.

To achieve this higher effective throughput demand, companies are now looking to several key techniques. These techniques being but not limited to; improvements to the physical layer, multiple-input, multiple-output (MIMO) technology, wireless interference mitigation, anti-jamming, and spatial cancellation.

A look at these various new techniques
First is the technique of modifying the physical layer. The goal of companies doing this, such as Silvus Technologies, is to make improvements at the physical layer such that the effective throughput is closer to the raw data rate. In the world of 802.11n, this means having throughput rates of 100 Mbps (with overhead) to a rate with no overhead of 300 Mbps. These improvements will mean that the magical goal of 150 Mbps will be achieved. More efficient PHYs enable WLAN systems to optimize the performance enhancing benefits of multiple-input, multiple-output MIMO technology in the 2.4 GHz and the 5.8 GHz ISM bands used today for WLANs.

Next is (MIMO) technology, although this technology has been deployed in WLAN and other applications. Companies are now taking MIMO to new levels of implementation and sophistication. MIMO is the use of multiple transmitters and receivers (multiple antennas) on wireless devices for improved performance. When two or more transmitters and two or more receivers are used, multiple simultaneous data streams can be sent, which significantly increase the data rate. Multiple receivers alone allow greater distances between devices. The IEEE 802.11n wireless standard uses MIMO to increase maximum speed to 100 Mbps and beyond. Companies such as Silvus Technologies have achieved a 4x4 MIMO configuration. These are more than just antenna solutions but complete baseband solutions which include the MIMO encoder and MIMO decoder. Studies on 802.11n devices reveal the short range throughput being measured at approximately 140 Mbps for 3x3 MIMO devices, at around 110 Mbps for 2x3 MIMO devices and close to 100 Mbps for 2x2 MIMO devices.

Wireless Interference mitigation is an art all by itself. High wireless throughput rates can be significantly degraded or completely disrupted by the presence of an out of network interferer. So what techniques are being developed to help with this problem? Companies are now developing techniques that are looking at improving the underlying radio system to improve its sensing and characterization functionality and reliably signal the presence of the interference, as well as its degree of sophistication (i.e. microwave oven or 802.11g). Next, they are looking at ways that will enable the radio to take evasive action in order to mitigate the effects of the interference and to ensure its throughput. There are several approaches being taken, with the first being the classical approach of sensing. This is simply the transmitter scanning the spectrum to identify holes where data communication can take place, and you take advantage of those spectral holes. The challenge is that in a broadband wireless system this sense and transmit notion will require more sophistication, because the variability of the interference environment in both space and frequency is much higher. The second approach is to use multiple antenna techniques to gather information about the spatial distribution of the interference.

Although one would think that wireless anti-jamming technologies would be used solely by the military and public safety entities, there is a growing need for commercial wireless systems to have this technology as well. The massive use of devices in the ISM bands has resulted in a number of potential threats to the integrity of wireless systems. So with the development of very high throughput wireless HD video transmissions, there will be even more vulnerability to jamming, i.e., signals that disrupt, reduce throughput or even prevent wireless distribution of data or video. This jamming will in all likelihood come not from intentional sources but by the dirty RF environment itself. So, there are companies looking to improve the receiver side of these wireless technologies by having a receiver capable of receiving a signal carrying data or video in the presence of jamming interference. These anti-jamming techniques process the received signal so as to determine a frequency, phase and amplitude of the jamming interference, and then through various technological approaches, they remove the jamming interference from the received signal and then demodulate the signal so as to recover the data.

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