Reply by dbd March 23, 20082008-03-23
On Mar 23, 12:46 pm, "alex65111" <alex65...@list.ru> wrote:
> A little clearly but not up to the end. > > Beamforming - some sensors coherently combined > and spatial diversity - some sensors and one of methods is maximal ratio > combining where input signals must be co-phased (coherently?) summed. > > Both there and there some sensors, both there and there coherently > combined (summed). > > And if a narrow beam selected only one direction of arrival of a signal > then should not be and deep fading?
Simple beamforming coherently combines sensor data in a physical space and produces one or more signals in beamspace. Spatial diversity processing can (but need not) include simple beamforming. In my example of a simple beamformer followed by additional spatial diversity processing, the additional processing can examine the beamspace channels and decide how to combine them. A simple approach would be to determine the best beam in each time block and use that beam for that time block. As beams grow and fade due to changes in multipaths, different beams would be best in different time blocks. A more capable processor might determine delays and amplitudes to apply to different beams to combine them in a manner with higher signal processing gain. Delays and amplitudes would be different in different time blocks. Spatial diversity processing can even be applied after some receiver functions have been performed. The receiver functions convert the signals from spatial or beam spaces to signal spaces. Spatial diversity processing can perform coherent combination in beam and other signal space domains. Simple beamforming provides coherent combination only for signals in the original spatial domain. Google 'spatial diversity' and you will get an abundance of different approaches. Dale B. Dalrymple
Reply by alex65111 March 23, 20082008-03-23
A little clearly but not up to the end.

Beamforming - some sensors coherently  combined 
and spatial diversity - some sensors and one of methods is maximal ratio
combining where input signals must be co-phased (coherently?) summed.

Both there and there some sensors, both there and there coherently 
combined (summed).

And if a narrow beam selected only one direction of arrival of a signal
then should not be and deep fading?

Reply by dbd March 23, 20082008-03-23
On Mar 23, 4:33 am, "alex65111" <alex65...@list.ru> wrote:
> Spatial diversity and beamforming solves one problem or each method solves > strictly own problem? > > In what these methods are similar among themselves and than differ?
Simple beamforming is used where there is a field that can be sampled and the samples combined coherently to improve signal to noise ratio (SNR). When there is a single direction of arrival, simple beamforming can improve SNR of low SNR signals. The sensors are placed in a field across which the signal to be processed is coherent. Spatial diversity techniques are used when there are multiple (and changing) directions (and times) of arrival. Then even in high SNR conditions a simple beamformer can experience deep fading. A simple diversity scheme could be to have multiple separated sensors with a receiver on each sensor and a combiner to select from the received data streams. This would be expensive because of the duplicated receivers. Many spatial diversity schemes are attempts to use signal and environmental characteristics to combine multiple sensor inputs at lower cost. Beamforming and spatial diversity processing are not mutually exclusive. A simple beamformer producing multiple independent beams could be placed in front of the simple multi-receiver spatial diversity processor above so that each beam replaced a sensor. In such a simple system, the beamformer provides coherent gain and the receiver/combiner stage provides non-coherent gain. Many spatial diversity schemes are not so simple to partition and describe. This description is based only on reception of a signal. Both beamforming and spatial diversity processing can become more complicated when you consider rejecting interference as well. Dale B. Dalrymple http://dbdimages.com
Reply by Rune Allnor March 23, 20082008-03-23
On 23 Mar, 12:33, "alex65111" <alex65...@list.ru> wrote:
> Spatial diversity and beamforming &#4294967295;solves one problem or each method solves > strictly own &#4294967295;problem? > > In what these methods are similar among themselves and than differ?
I am not sure 'spatial diversity' is a method - from the sound of it I would suspect it is a property of a scenario. If the sources are far apart (in terms of Direction of Arrival) the scenario is 'spatially diverese' and a beamformer might work better than if the sources are located close together. Rune
Reply by alex65111 March 23, 20082008-03-23
Spatial diversity and beamforming  solves one problem or each method solves
strictly own  problem?

In what these methods are similar among themselves and than differ?