URH Full Digital Optical Fiber Distribution System Wireless Solution

Currently, the wireless signal coverage method used in subways is basically built by multiple operators using POI high-power signal sources and coaxial feeders. At present, various communication requirements are increasing day by day. Various mobile phone communications, wireless intercoms, wireless Internet access and other functions require the construction of multiple independent systems, resulting in tight computer room resources, difficult construction, complex management and maintenance, and redesign and planning are required when adding new functions.

URH is a new generation of wireless solution proposed by ADC to improve wireless capacity, coverage and flexibility and meet customer needs. The wireless room divides the wireless signal to improve the wireless capacity and distribution range, and the downlink signal is adaptively adjusted to compensate for the signal attenuation. It is an intelligent signal coverage system (as shown in Figure 1).

URH distributes RF signals to the areas where they are needed through fiber transmission technology. URH digitizes all designated RF bands and transmits them in digital mode through dark fiber or millimeter wave (MMW) links, and can reconstruct signals in full bandwidth regardless of the modulation technology used at the far end. ADC's digital RF transmission allows RF signals to be replicated in all dynamic bandwidth ranges regardless of link length to improve data throughput. As service providers also deal with the upgrade from 3G to 4G, high data rate broadband services, networks using URH high-speed links are ready for upgrades for service providers.

Overall design idea of ​​URH solution
URH remote unit module is placed in each station, and no machine room is required.
The sector-based zoning design reduces the number of stations and switches.
It supports multiple operators and multiple carriers, and supports later upgrades to 3G/4G.
Only one central machine room is required, and base stations are placed centrally.
It is realized through the loop function equipment of the system itself, and has an automatic switching function. A loop is formed between the URH main end and the 8 URH remote ends of each cell in turn, and automatic switching occurs when a fault occurs.
Technical features of URH solution
The system adopts all-digital fiber distribution technology, and long-distance transmission is noise-free.
Multiple systems are transmitted through digital optical fiber.
Multiple lines in a single machine room.
A single system supports multiple communication systems and multiple networks in the 800MHz, 900MHz, and 2100Hz frequency bands (as shown in Figure 2).

Figure 2 Schematic diagram of the URH scheme structure

Comparison between URH solution and POI solution

Equipment investment comparison

In terms of the number of computer rooms, the POI solution has one for each station, while the URH solution has one for multiple stations. The number of computer rooms and supporting facilities such as air conditioners is required for each station in the POI solution, while the URH solution only needs one centralized computer room. In terms of base station signal sources, the URH solution does not require high-power base station signal source equipment, but only low-power or micro-power base station signal sources, which can save a lot of resources in terms of signal sources.
Since it is a centralized base station placement solution, there is no need to design a base station for each station, so the transmission equipment can be saved 100%.

Distributed System Performance Comparison

The POI solution uses analog RF power push technology, while the URH solution uses optical fiber digital distribution and remote technology. The former networking method requires a switch when the train passes each station, which is prone to call drops and reduced base station capacity. The latter adopts a large-area system with no switching between 4 to 5 stations, ensuring the dynamic allocation and scheduling of the system capacity. In addition, the noise coefficient of the digital distribution system is much smaller than that of the analog RF equipment, which equivalently increases the system capacity in mobile communications based on the CDMA system, reduces the mobile phone transmission power, and extends the battery life of the mobile phone. In the later optimization process, it is difficult to plan and allocate capacity in POI sub-cells. The URH base station centralized placement solution can flexibly realize carrier scheduling through the central machine room. It can also realize daisy chain and self-healing loop functions through optical paths, increasing system reliability.

Comparison of engineering construction

POI is large in size and consumes a lot of power. It needs to be amplified separately for both upstream and downstream. If the power at the end is insufficient, it needs to be amplified by splitting and splitting. The URH solution has a 3U high rack with 19 storage at the front end, and can be expanded by plugging in cards. The back end is flat and can be placed in the tunnel, and the construction is simple and convenient.
Therefore, in the context of large-scale construction of urban rail transit in China, the adoption of the URH solution is an energy-saving, environmentally friendly and high-quality solution that is easy to upgrade and maintain later, which saves supporting resources, saves energy consumption and improves the quality of network services.