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Gin: Gigabit Indoor Wireless
Wireless communication systems enable tetherless communication between a variety of nodes ranging from humans to computers.
They may roughly be classified by their geographical coverage area.
Cellular systems provide global coverage, international roaming and unconstrained mobility.
Wireless access systems in contrast support locally constrained tetherless connectivity and mobile access to a backbone network (typically the Internet).
The slow take-off of UMTS as opposed to the explosive growth of 802.11 based WLANs indicates the growing importance of wireless access.
Currently most WLAN nodes are portable computers, which makes throughput the major QoS parameter.
For this reason the application of MIMO technology to IEEE 802.11 is of major interest.
It is expected, that future WLANs will be used by a more heterogeneous range of nodes.
Spatial multiplexing provides scalability with acceptable hardware (IC) reuse across nodes.
Thus a future WLAN has to integrate nodes with varying antenna array size.
Due to the ubiquitous deployment we expect a much higher node density than in current WLANs.
The availability of bandwidth makes operation beyond 5 GHz mandatory (e.g. in the 17/24GHz bands).
The figure illustrates a major problem of future WLANs. We consider a MIMO link with the following constraints:
- fixed physical dimensions (form factor) of the source and destination antenna arrays
- fixed path length
- fixed total source transmit power
- no channel state information (CSI) at the source
- no antenna coupling
As we increase the carrier frequency, the possible number of λ/2 spaced antenna elements thus roughly is proportional to the square of the carrier frequency f.
On the other hand the free space path loss increases proportionally to the square of f.
Without scattering (red line: “no scattering”) it is not possible to achieve a spatial multiplexing gain; the array gain of the destination antenna system however compensates the increasing path loss and the capacity is independent of the carrier frequency (without channel state information at the source, we cannot realize a transmit antenna array gain).
In rich scattering (blue line: “rich scattering”) the system achieves the full spatial multiplexing gain.
Due to the increasing path loss the capacity increase is less than one would expect from the rank of the channel matrix (note, that the transmit power per source antenna element is inversely proportional to the number of elements).
Nevertheless the capacity gain is very appealing. We further see, that under these idealized constraints an increase of the carrier frequency not necessarily reduces the range (coverage) for a given transmit power.
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