Indoor Coverage, the Key to a Successful 3G Network

The advent of 3G era allows more and more subscribers to enjoy the extensive and continuous multimedia and data services anytime and anywhere. To improve the quality of 3G services and attract subscribers, network operators must first solve the challenging problems in door coverage, capacity and network performance. As the 3G frequencies have a poor penetration and deffraction capability, signal loss in indoor environments is significant and wave distortion is severe. As a result, more blind spots occur in a 3G network than in a 2G network.

To date many 3G networks have been put into commercial operation worldwide. Top operators have shifted their focus on the relationship between the network deployment, the behavior of subscribers, and the effect of service promotion. Since 2003, it has become a widely-accepted notion that the indoor coverage system plays a pivotal role in the development of a 3G network. For example, after analyzing the behavior data of 3G subscribers, NTT DOCOMO found that it was important to improve the indoor coverage quality, so it further deployed over ten thousand sites to achieve better indoor coverage. According to the statistics made by NTT DOCOMO, the network capacities inside buildings increase by 1.43 times after the optimization.

Top mobile operators now definitely understand the importance of the indoor coverage and spare no effort to achieve the best coverage effect possible. What kinds of obstacles stand in the way to perfect indoor coverage and how to remove the obstacles? The following provides analysis and suggestions.

Challenges Facing Indoor Coverage

Firstly, indoor site acquisition becomes a tough question for many operators, especially in densely populated areas such as Hong Kong and other metropolitans in Japan and European countries.

Secondly, the purpose of indoor coverage is to meet both the coverage and the capacity requirements of the voice and high-speed data services. Traditional indoor coverage solutions, however, have the problems of signal source introduction and CAT5/6 transmission loss and require extensive cultivation. Even so, they can hardly meet the capacity and quality requirements of 3G services and are absolutely not the choice for 3G networks which aim at delivering real-time multimedia and data services to subscribers, especially VIP subscribers.

In addition, facing increasingly severe market competition and accelerated evolution of technologies, more and more operators realize that it is important to have a cost-efficient indoor coverage system that can be flexibly and effectively deployed and optimized. With the increase of 3G subscriber base and wide acceptance of high-speed services, requirements for system capacity become urgent. At present, coverage effect, capacity expandability and ease of maintenance of indoor coverage systems have become the overriding concerns of some 3G network operators, because these factors have much to do with their TCO and are key to their competitive edge.

Evolution of Indoor Coverage Solutions

As power distributors, couplers, attenuators, and amplifiers cause signal loss, noise, external accumulation, and non-linear degradation, the receive sensitivity of antennas becomes low and thus system capacity and network performance are affected. In addition, thick and heavy RF cables are difficult to deploy inside buildings and usually cause damages to buildings, adding the difficulty to site acquisition. Such traditional indoor coverage system has been widely used, but it cannot satisfy the present networking development and challenges facing network operators.

To solve these problems, a simulation optical distributed system was developed, in which thick RF cables are replaced by optical fibers. This system converts RF signals into optical signals so that they can be transferred by the optical fibers. The optical signals are converted back to RF signals at the other end and are magnified by the Remote Access Unit.

Disadvantage of this system is that one system supports only one cell or carrier, and the problems of capacity and the high cost of indoor deployment remain unsettled. Especially when the network evolves to an IP network, where large amount of data must be transferred at high speed, the system also encounters similar challenges such as site acquisition difficulty, restricted capacity, and cost-effectiveness. The development of 3G networks calls for a new indoor coverage solution.

In this situation, the Huawei digital indoor distributed NodeB system, iDBS, comes into light to answer the present and future demands.

Huawei iDBS, Innovative Solutions for Indoor Coverage

The Huawei iDBS solution integrates the digital technology, distributed NodeB technology, and intelligent CPU and DSP processing techniques. It comprises a series of Huawei indoor NodeB products, including the BBU3806, RHUB3808 and Pico RRU3801, as shown in Figure 1.

Figure 1  Structure of the iDBS solution

The Pico RRU (pRRU) is a low-power RF module. It is light and compact (equal to the size of normal portable computer) and best suits complicated indoor environments. The RHUB is a converge unit that is developed to add the flexibility of the solution. It converges the signals from the Pico RRUs to reduce the number of fibers or CAT5 cables and BBU ports. The RHUB also remotely provides -48V power to the BBU and Pico RRU. The BBU and RHUB are packed in standard cabinets (1U high and 19 inch wide). This makes their installation and transportation easy and convenient, just like a normal router.

Using the iDBS solution, operators can easily achieve best quality coverage inside buildings by flexibly combining the elements of the solution to adapt specific conditions. The Pico RRU can be configured with scramblers flexibly. That is, one scrambler or cell can be configured with one Pico RRU or several Pico RRUs. This enables flexible capacity or coverage area adjustment.

The Pico RRU is suitable for various application scenarios. As Figure 2 shows, the networking is simple and no Macro NodeB is required

Figure 2 Example of iDBS application

Benefits of the iDBS Solution

Reduced site acquisition difficulty

The iDBS uses fibers and CAT5/6 cables instead of thick and heavy RF cables. This protects building to the maximum degree and thus reduces the difficulty of site acquisition. To reduce deployment cost and difficulty, the RHUB and RRU are connected using CAT5 cables, and the BBU and Pico RRU are connected using fibers.

High capacity and wide coverage

The iDBS system can support 12 cells per carrier and can connect as many as 192 Pico RRUs and 768 antennas. If one antenna transmits 0 dBm power and covers about 400 square meters, the iDBS system can cover more than 300,000 square meters.

Upgraded network performance

The performance of traditional indoor coverage solutions largely depends on the processing capability of outdoor NodeBs. As a normal NodeB supports only 5 codes, the HSDPA performance is limited and the advantage of indoor coverage is not fully utilized. In comparison, the iDBS solution supports full-performance HSDPA using 15 codes and the maximum data throughput can reach 14.4 Mbps. Tests showed that the data throughput of a full-performance HSDPA network is 3 times that of a normal HSDPA network and such a network can support most of the applications required for VIP subscribers.

Better coverage effect

Traditional indoor coverage systems use a lot of cables and power distributors, and as a result, a significant amount of power from the UE and the Node B are lost in the distributed system, affecting the coverage effect of the whole system. The iDBS minimizes the use of cables and power distributors to fully utilize the transmit power.

For example, in a typical office building, the iDBS allows the UE to transmit at a level 1000 times less than that allowed by a traditional system, while maintaining the specified QoS. This greatly reduces undesired radiation, secures better coverage effect, and prolongs battery life.

Pertinent investment based on precise hot spot location

The iDBS solution provides an intelligent, graphic-based uniform network maintenance tool in comparison to the simple monitoring ways available in a traditional system. Using this tool, operators can carry out comprehensive monitoring on the traffic density and equipment operation. This helps operators precisely locate hot spots before making corresponding fine adjustments.

Easy subscriber data migration

Nowadays more and more factors can affect people's business behaviors, resulting in frequent changes of building functions and service requirements. The iDBS system, which exhibits the features of flexible engineering and strong adaptability, allows for VIP data transfer through mere data configuration, without the necessity of network rebuilding.

Easy network expansion

3G frequency resources that can be used by a network operator are limited and that can be used for indoor coverage are even more scarce. The indoor capacity expansion of 3G networks is usually achieved by cell splitting. In a traditional indoor system, you must adjust the cabling and configuration of the system to achieve cell splitting. The iDBS solution saves the physical work of re-cabling, and cell splitting can be achieved through mere data adjustment.

Featuring simple deployment, high capacity, flexible configuration, easy optimization, and centralized maintenance, the iDBS system manifests the development trend of indoor coverage solutions and is sure to lead the way in indoor network deployment. Huawei, by leveraging its advanced technologies and initiatives, is committed to carrying on and bringing out more cost-effective solutions that address customers' real concerns.