Tuesday, February 14, 2012

Frequency reuse

The key appropriate of a cellular arrangement is the adeptness to re-use frequencies to admission both advantage and capacity. As declared above, adjoining beef accept to use altered frequencies, about there is no botheration with two beef abundantly far afar operating on the aforementioned frequency. The elements that actuate abundance reclaim are the reclaim ambit and the reclaim factor.

The reclaim distance, D is affected as


where R is the corpuscle ambit and N is the amount of beef per cluster. Beef may alter in ambit in the ranges (1 km to 30 km). The boundaries of the beef can aswell overlap amid adjoining beef and ample beef can be disconnected into abate beef 1

The abundance reclaim agency is the amount at which the aforementioned abundance can be acclimated in the network. It is 1/K (or K according to some books) area K is the amount of beef which cannot use the aforementioned frequencies for transmission. Common ethics for the abundance reclaim agency are 1/3, 1/4, 1/7, 1/9 and 1/12 (or 3, 4, 7, 9 and 12 depending on notation).

In case of N area antennas on the aforementioned abject abject site, anniversary with altered direction, the abject abject website can serve N altered sectors. N is about 3. A reclaim arrangement of N/K denotes a added analysis in abundance a part of N area antennas per site. Some accepted and actual reclaim patterns are 3/7 (North American AMPS), 6/4 (Motorola NAMPS), and 3/4 (GSM).

If the absolute accessible bandwidth is B, anniversary corpuscle can alone use a amount of abundance channels agnate to a bandwidth of B/K, and anniversary area can use a bandwidth of B/NK.

Code analysis assorted access-based systems use a added abundance bandage to accomplish the aforementioned amount of manual as FDMA, but this is compensated for by the adeptness to use a abundance reclaim agency of 1, for archetype application a reclaim arrangement of 1/1. In added words, adjoining abject abject sites use the aforementioned frequencies, and the altered abject stations and users are afar by codes rather than frequencies. While N is apparent as 1 in this example, that does not beggarly the CDMA corpuscle has alone one sector, but rather that the absolute corpuscle bandwidth is aswell accessible to anniversary area individually.

Depending on the admeasurement of the city, a auto arrangement may not accept any frequency-reuse in its own city, but absolutely in added adjacent cities, the aforementioned abundance can be used. In a big city, on the added hand, frequency-reuse could absolutely be in use.

Recently aswell erect frequency-division assorted admission based systems such as LTE are getting deployed with a abundance reclaim of 1. Since such systems do not advance the arresting beyond the abundance band, inter-cell radio ability administration is important to coordinates ability allocation amid altered corpuscle sites and to absolute the inter-cell interference. There are assorted agency of Inter-cell Arrest Coordination (ICIC) already authentic in the standard.2 Coordinated scheduling, multi-site MIMO or multi-site axle basic are added examples for inter-cell radio ability administration that ability be connected in the future.

edit Directional antennas

Cellular blast abundance reclaim pattern. See U.S. Patent 4,144,411

Although the aboriginal 2-way-radio corpuscle building were at the centers of the beef and were omni-directional, a cellular map can be redrawn with the cellular blast building amid at the corners of the hexagons area three beef converge.3 Anniversary belfry has three sets of directional antennas aimed in three altered admonition with 120 degrees for anniversary corpuscle (totaling 360 degrees) and receiving/transmitting into three altered beef at altered frequencies. This provides a minimum of three channels (from three towers) for anniversary cell. The numbers in the analogy are approach numbers, which echo every 3 cells. Ample beef can be subdivided into abate beef for top aggregate areas.4

No comments:

Post a Comment