Island effect

In electronic circuits, island effect of a certain region refers to the circuit is designed to be with current access and the actual no current through the phenomenon. In a communication network, the island effect is wireless mobile base station coverage there may be one kind of phenomenon.

principle

The capacitors in tandem with the circuit, only deoxidization device connected the two plate (note: not the same capacitor plate) have current flow (charge exchange), other plate of total charge is constant, so called island. Island is a kind of electrical phenomenon, occurred in part of the power grid and the main power disconnected, and this part grid entirely by photovoltaic system to power supply. In international photovoltaic (pv) grid standardization on the topics that is still a point of debate, because the island will damage the public and electric power company maintenance personnel and safety of power supply quality, in manually or automatically switch to the island reclosing power grid to power supply from time to tome may damage the equipment. So, inverter usually contains prevent island effect device. Passive technology (detection grid voltage and frequency changes) in balancing the load is very good conditions electrify and again electrify two circumstances of itsself prevent enough and, therefore, must be combined with full active technology, active technique is based on the sample frequency shift, the flow of electric current impedance monitoring, phase jump and harmonic monitoring, positive feedback method, or the unstable current and phase on the basis of the controller. Now, there are many preventing measures, in the world already had 16 patent, some have been obtained, and some are still in the process of application. Among them some methods, such as monitoring network flow of current pulse was proved to be convenient, especially when many sets of the inverter parallel work, can reduce power quality, and because many sets of inverter mutual influence on his island detection negative effects. In some cases, for voltage and frequency range of work limits becomes wider, and installation workers can usually through software to set up these parameters, even ENS (a monitoring device, in Germany is mandatory) in order to succeed in the power grid work, weak can turn it off.

Island effect laboratory

In general it is used resonant load simulation circuit, and at the same time defines a quality factor, "Q - factor". Nevertheless, these experiments is hard to run, especially those high power inverter, they need a great deal of laboratory. Test the circuit and the parameters according to different countries differ, test results depends largely on the student's technical level.

Now has carried out some research to assess island effect and its associated risk of all sorts of possibilities, studies have shown that for low density of photovoltaic power systems, in fact island is impossible, because the load and power ability is impossible to match. But, for with high density (pv) power system of power grid part, active island effect protection method is necessary, at the same time complementary with voltage and frequency control, to make sure the pv brings risk to the extremely small, the data must be and not take the grid in photovoltaic number is expected to compare electrocuted. Most photovoltaic inverter simultaneously with active and passive island protection, though not many photovoltaic (pv) grid smashed into the examples, but to this aspect, foreign standards no relaxation.

Island effect is the base station coverage problem, when base covered in large surface or mountainous terrain, and other special, because the water or mountain reflection, make the base station in the original coverage unchanged on the basis of, in the distance appear "enclaves," and with the handover relationship between adjacent base station however because of terrain prevents the cover, thus causing "less than enclaves" with adjacent base station between no switching relations, "ship" thus became a lonely island, when the phone is occupied "enclaves" in the covered area of a signal, very easy because no switching relationship and cause to drop words.

Island effect wireless communication

Serving cells due to various reasons (wireless transmission environment too good, base station position too high or antenna obliquity smaller), leading to cover is too heavy to the adjacent region coverage inside, cause in some area of coverage appear a lonely area (the so-called umbrella covering), this lonely regional geographically without adjacent area, similar to the "island". If the mobile station move in this region, with no adjacent area, the mobile station cannot switch to other district lead to drop words happen.

"Gu island effect" appear more in network expansion after. With the new base station of GeJie net, need to the original area coverage to adjust, but area coverage contraction fast can cause two village switching take cover is bad, conversely, easy to create "island effect".

Usually to solve the problems of the devices can be through a lot of DT test to discover a problem, generally can reduce district's coverage and increase adjacent area list.

Use redundancy eliminating the "island" neighboring relationship, reduce to drop words.

Wireless optimization mainly resolves to drop words, frequency interference, switching problems and and network congestion, talk here redundant adjacency relations with lower drop words method. Cause to drop words many reasons, such as with inner out-of-band interference, the frequency of the handover relationship shall surely wrong leakage, hardware malfunction, covering enough to drop words, the weak signal user mobile phone off electricity, etc. This many of these questions have colleagues do discussed. Here want to talk about in switching relationships define the method to solve to drop words.

Because of our network covers have relatively good, open the frequency hopping, frequency interference between a much smaller than before. In actual work often find many drop words because handover relationship is caused, the following examples:

Under normal circumstances, B of the base of the base CELL3 only define A CELL1, CELL2 for neighboring cells, so also is commonly in the CDD definition, we often think of the base B artificial CELL3 would only meet with A base station of CELL1 and CELL2 have switching. But in actual often found B road test of the base stations across A signal and ran to A CELL3 covering area of the base, in local forms the signal strength than A standing CELL3 and become the strongest village, namely common "gu island effect". Especially in the base station densely populated, there will be many repeat cover, form many "small island" (as shown in the small circle). Because these islands area is lesser, and as wireless environment changes, if road test in accordance with fixed line have been walking words, it is difficult to find their presence. Only just in these small island in time, mobile phone re-election on B area CELL3, right now you telephone and mobile, usually because there is no better neighboring cells to drop words. On the other hand, if still have A base station C, A base station located between B and C, then when A standing congestion or be occlusion, from B: CELL3 C base station will be of no direct handover relationship. Accordingly, from base stations to C B mobile users will likely because cannot find good village switch or still cut to a poor village and eventually to drop words. Because these "little island" has the strong concealment, cause we often ignore it. In the index and is often difficult to reflect.

Commonly used solution have to increase obliquity, reduce the antenna transmission power or with the maximum limit TALIM parameters residential coverage, but these methods are all has its drawbacks. In the practical work, we often use add set redundancy one-way handover relationship measures to solve, such as in the above example, can add CELL3 to set B: A: CELL3 or C: CELL1, CELL2 unidirectional switching relationships, and even add set B: CELL3 C three village of unidirectional handover relationship. However, due to the high frequency reuse degree now, may appear A: CELL3 and C: CELL3 BCCHNO same situation, then add set handover relationship still need to replace one of the district's BCCHNO, avoid neighboring cells BCCHNO identical.