Combining diversity is a technique applied to combine multiple signals received from a diversity receiver into one enhanced signal.
Video Diversity combining
Various techniques
Berbagai teknik menggabungkan keanekaragaman dapat dibedakan:
- Penggabungan gain-sama: Semua sinyal yang diterima dijumlahkan secara koheren.
- Penggabungan rasio-maksimal sering digunakan dalam sistem array-bertahap besar: Sinyal yang diterima diberi bobot sehubungan dengan SNR mereka dan kemudian dijumlahkan. Hasil SNR menghasilkan di mana adalah SNR dari sinyal yang diterima .
- Switching menggabungkan: Penerima beralih ke sinyal lain ketika sinyal yang saat ini dipilih turun di bawah ambang batas yang telah detentukan. Ini juga sering disebut "Scanning Combination".
- Penggabungan pilihan: Dari sinyal N yang diterima, sinyal terkuat dipilih. Ketika sinyal N independen dan didistribusikan Rayleigh, keuntungan keragaman yang diharapkan telah ditunjukkan menjadi , dinyatakan sebagai rasio daya. Oleh karena itu, setiap keuntungan tambahan berkurang dengan cepat dengan meningkatnya jumlah saluran. Ini adalah teknik yang lebih efisien daripada beralih gabungan.
Sometimes more than one merging technique is used - for example, imaging is fortunate to use the election merge to choose (usually) the best 10% image, followed by the same gain incorporation of the selected image.
Other signal combination techniques have been designed to reduce noise and have found applications in single molecule biophysics, chemometrics among other disciplines.
Maps Diversity combining
Combine time
When the focus is on wireless transmission of longer signal sequences, such as Ethernet packets, the specific performance characteristics of diversity advantages in parallel redundant and wireless transmission systems can be observed. To "combine time", data packets are overloaded and simultaneously sent over parallel paths. At the receiving end, exit from the first arrival packet branch is selected and immediately processed towards the final application. Further copies of the package-if arriving-are discarded. This type of post-decomposition combining is called "timing", since significant performance improvements are obtained through the immediate processing of the first arrival packet.
Switch merge two-way radio samples
On landline-cellular radio, where radio-mounted and hand-held radio stations communicate with a single frequency station, the diversity of space is achieved by having multiple receivers in different locations. Combining diversity, or voting , in a two-way radio system is a method of increasing the range of talks from walkie-talkies and mobile cellular radios.
The receiver is connected to a device called a voter or voter counterpart.
The voting apparatus evaluates all received signals and picks up the most usable signals. In the repeater system, the selected signal will be retransmitted. In the simplex system, it goes to the console speakers at the base station. Audio from unselected recipients will be ignored. The polling comparator in an analog FM system can switch between receivers in a matter of tithes - or one hundredth of a second, (faster than a syllable). As long as the signal is understood to one recipient in the system, repeated audio, or audio sent to the console speaker, will be understandable.
In this setting, the recipient at a remote location is connected to a voting appraiser by a private telephone line, a channel in a D4 channel bank on a DS1, or an analog microwave baseband channel.
How the signal is evaluated
The earliest voting appellers rely on the encoded tones on separate audio channels, requiring each receiver location to have a 4-wire or two-way audio circuit. The tone tone changes to represent the received signal level, or the FM receiver's limiter voltage, on the remote receiver. This works poorly because it does not take into account the noise of microwave baseband or noisy telephone company circuitry.
New comparison comparisons compare signal-to-noise ratios in comparison to polling, accounting for end-to-end noise, poor phone lines, poor level discipline, and best diversity acceptance channels.
Walkie-talkie range
When communicating with handheld radios (walkie-talkies), base stations generally speak farther than they can receive. Voting between multiple receivers at different locations increases the likelihood that one receiver will obtain usable signals from a two-way radio in a system.
Interference reduction
Combination diversity reduces one possible one-point failure: any single recipient failure, or local interruption to a single recipient, will not block reception throughout the system. The equipment site can accommodate many radio transmitters and receivers. One site is subject to local, site-specific interference signals. This disturbing signal can come and go when the transmitter lives and dies.
A potential problem with recipients located on high-elevation receiving sites is that they can obtain signals from distant districts, prefectures, or other provinces. These unwanted and remote signals can become stronger than the desired signal from the local walkie-talkie. The remote signal can block local weak signals in some cases. Having multiple recipient sites increases the likelihood that one site will receive a local signal in the presence of a remote, undesirable one. Selective dialing can eliminate the user having to listen to the audio of the remote signal even though the remote signal is within reach of one or more recipients.
Coverage
A minimum of 95% coverage is quoted in the literature for critical or emergency two-way radio system services. One definition of system coverage is the standard TSB-88A Telecommunications Industry Association (TIA).
Vote-lock or vote-and-hold option
Most installations using diversity combination equipment continue to evaluate the best received signal to all other signals. Throughout the length of transmission received, the comparator can replace the receiver as often as every tenth of a second. As walkie-talkie users cause the signal to fade by turning their heads, or a passing tractor-trailer rig blocking their signal on the receiving site, the merging unit quickly changes to a different recipient.
In some installations, diversity combination tools are configured to lock recipients. For example, in some regional and rural coverage systems, each recipient encompasses a unique geographic area. Not much overlap. If the system consists of two sites, north and south, it will select the better of the two and stay locked on the receiver until the transmission ends. This works better with cellular radio because their signal strength tends to be stable.
In some cases, voting and hold is used to direct the selection of the transmitter. Consider the case of a regional system with two base stations: north and south. If the diversity that merges the equipment selects "north," when the dispatcher presses the transmission button, the north transmitter will become the key. Called transmitter steering , this should automate the selection of the transmitter in the system where more than one transmitter site is available. In some cases, it does not work very well.
In mobile data systems, voice lock options are preferred because the constant switching between receivers results in the loss of data packets. The diversity of combining switching equipment is fast enough so that syllables are not lost but not fast enough so the bits are not lost. The mobile data system usually comes from modems in cellular radio. Cellular radio typically generates solid signals to more than one receiving site, so the signal strength is strong enough for voice lock to work properly.
See also
- Transmit diversity
- Antenna diversity
- Synthesis openings
- Diversity of cooperation
- Smart antenna
References
Further reading
- L.-C. Lin, M. Guo & amp; K. T. Wong, "Selection of Two Branches in Wireless Space-Diversity Reception: Upper Limit for Output Power," IEEE Transactions on Communications, vol. 60, no. 2, p. 537-546, February 2012.
Source of the article : Wikipedia
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