Ericsson TD-LTE/GSM joint station construction plan

Most of the commercial deployments of TD-LTE in the world have adopted the construction method of co-station with the original TDD system. The TD-LTE scale test recently launched in China also chose the TD-SCDMA networking method. However, in the face of the scale-up test that TD-LTE is about to begin, the problem of insufficient resources of the TD-SCDMA site is particularly prominent. This paper introduces the TD-LTE/GSM co-site construction plan proposed by Ericsson recently, and demonstrates its feasibility. The system coverage and capacity are analyzed mainly through system simulation, and suggestions for sharing the dual-frequency antenna scheme are proposed. Finally, the RF isolation requirements of TD-LTE/GSM coexistence are analyzed, and the solution of introducing low loss and high suppression combiner is introduced. Through the concept verification of the single station on the live network, the results show that the scheme ensures the stability of the GSM1800 and the performance of the TD-LTE has no obvious loss.

With the end of the second phase of the TD-LTE scale technology test, the TD-LTE industry chain is maturing. The expansion of the scale of TD-LTE network deployment will become the focus of the next phase.

In the 6-city scale technical test, the continuous networking capability of deploying TD-LTE based on the TD-SCDMA site in the urban area was verified, including two antennas and eight antennas.

The test results show that TD-LTE can achieve continuous coverage and co-frequency networking whether it is 2 antenna or 8 antenna scheme.

This attempt is similar to the idea that most operators in the world choose to deploy LTE systems based on the original system in the LTE commercial deployment process.

At present, most of the commercial experience of foreign TD-LTE adopts the scheme based on the original system site, for example, the existing PHS and WiMax networks. These solutions can effectively reduce network deployment costs, speed up construction progress, and help operators to protect their investments in the early stage. However, this idea also faces a series of challenges. The more typical problems include:

"Because of the technical differences between systems, the coverage and interference caused by different antenna configurations." Because multiple systems share some network elements (such as antennas and RF units), the coupling between systems is too tight, resulting in system performance degradation. , and problems that cannot be optimized independently.

In China, the construction of TD-LTE networks based on TD-SCDMA is also faced with the problem of limited site resources and insufficient network density.

Compared with the TD-SCDMA network, the GSM network has been built for more than ten years, and its scale advantage is obvious, especially in the site storage, which is obviously better than other systems. If the TD-LTE network can be built using the GSM site, it will bring huge economic benefits to the commercial deployment of TD-LTE in China.

It also paves the way for the deployment of TD-LTE for the traditional FDD operators in the world, which will greatly expand the international market space of TD-LTE.

In view of this, this paper discusses several technical issues of deploying TD-LTE based on GSM network, including system coverage and capacity analysis, antenna solution and multi-system coexistence isolation problem.

First, the coverage problem of TD-LTE/GSM co-site construction is based on whether the existing GSM network (station spacing) can meet the requirements of TD-LTE for continuous coverage and cell edge rate. The simulation results below are based on the partial site address and actual station height in a city's GSM live network. The coverage effect of the 2 transmit and receive antenna configurations is adopted. The probability that the cell RSRP value is better than -110 dBm is 95% or more, which satisfies the basic continuous coverage requirement. (As shown in Figure 1).

The number of GSM sites in the actual network is about 20% to 30% more than the base station used for the simulation. Therefore, sharing the GSM website address is completely feasible to meet the coverage of the TD-LTE network, and can support the network to further improve the performance and the need for a more dense site when expanding.

In addition, if the existing TD-S equipment is upgraded to TD-L, due to the limitation of broadband amplifier, the specific subframe needs to be selected (3:9:2), and the downlink theoretical peak rate/effective capacity is reduced by 25% compared with the ideal configuration. , network capacity and performance loss is obvious. When the scheme is built with the GSM co-site 2 antenna, it is not necessary to share the power amplifier with the existing equipment, so the optimal slot/subframe configuration can be flexibly selected, and the spectrum resources can be effectively utilized, thereby achieving better network performance and capacity. .

In the actual network, if considering the interference factor caused by the traffic load, the above GSM co-station scheme performs better in terms of actual rate and cell capacity. It can be seen from the above analysis that the TD-LTE and GSM co-station solution not only meets the coverage requirements of China Mobile when deploying TD-LTE, but also has great advantages in terms of performance and capacity.

TD-LTE/GSM antenna solution

From the perspective of ensuring the performance of TD-LTE networks, it is the preferred solution to build a new antenna for TD-LTE based on the GSM site.

From the current deployment situation of other operators in the world, most of them adopt the scheme of co-site and independent antenna. This solution facilitates independent optimization between systems and reduces the interaction and constraints between systems, such as: daily operation and maintenance, network expansion and so on.

However, in engineering practice, it is often necessary to share antennas with multiple systems due to limited surface. This chapter focuses on the solutions for TD-LTE and GSM shared antennas.

The choice of TD-LTE/GSM co-site antennas is mainly considering the combination of TD-LTE/GSM frequencies. Assume that the TD-LTE outdoor application frequency band is 1.9 GHz and 2.6 GHz. In the current network, the frequency used by the GSM system is 900MHz and 1.8GHz. Due to radio propagation characteristics and network bearer factors, it is recommended to build TD-LTE and GSM1800 stations.

Although TD-LTE has two different antenna configurations of 2 and 8, the TD-LTE is deployed based on GSM1800, and the shared antenna is required, the 2-antenna scheme is obviously more reasonable and feasible.

The FDD-LTE network deployed in Europe uses a solution that shares the antenna with 2 antennas and GSM1800. In the antenna sharing scheme, in addition to meeting the required multi-frequency requirements, there is no special requirement for the technical specifications of the antenna itself, but in order to reduce the coupling degree between systems, it is recommended to satisfy the design of the independent ESC of each system as much as possible. At present, antenna manufacturers at home and abroad can provide such dual-polarized, multi-band, independent ESC antennas, and have been commercially available. Assume that both GSM900 and GSM1800 currently use separate antenna systems. The TD-LTE and GSM1800 co-site construction plans are as follows:

Dual-polarized dual-band dual-coupling commercial antennas are available. These antennas have 2 pairs (4) of antenna ports. The signals of the two sets of antenna ports can be adjusted manually or remotely to reduce the electric downtilt angle. Relatively independent optimization. Such antennas on the market include dual-frequency antennas 1710-2170 MHz/2300-2690 MHz and wideband antennas 1710-2690 MHz/1710-2690 MHz. Independent ESC can be realized.

TD-LTE/GSM coexistence RF analysis

At present, China Mobile's GSM1800 and TD-SCDMA are mostly built with GSM900. Whether it is from TD-SCDMA or GSM evolution to support F-band TD-LTE, it is necessary to consider the isolation problem with GSM co-site. The following is a theoretical analysis of the isolation between the two systems:

TD-LTE interference to GSM1800:

Spurious interference: According to the 3GPP specifications, the spurs of TD-LTE falling in the receiving band of GSM1800 are: -98dBm/100kHz; considering the sensitivity of GSM receiver is -110dBm, the isolation between the two systems is required to be small.

Blocking interference: According to the 3GPP specifications, considering that the blocking index of GSM outside the receiving band is 0 dBm, the required isolation requirement is small.

GSM1800 interference to TD-LTE:

Spurious interference: The spurious emission requirements of the GSM system in the TD-LTE frequency range (1880 to 1920 MHz) when the co-station is not specified in the 3GPP specifications. If there is no special consideration for co-site support, the general GSM products can meet the sag index requirements of -30dBm/MHz.

Then, in the case that the performance of the TD-LTE receiver is not significantly reduced, the required isolation requirements are strict.

Blocking interference: According to the 3GPP specifications, the blocking index for LTE and GSM co-station is +16 dBm; assuming GSM maximum transmit power is 49 dBm, the required isolation is small. From the above analysis, we believe that the main problem of interference between GSM and LTE systems is the interference of GSM downlink transmission spurs on TD-LTE uplink reception. When considering network isolation or filter coupling fading, it is required for network deployment. The isolation requirements are stricter. According to this requirement, for the space isolation of the antenna to meet the requirements, the required horizontal space isolation or vertical isolation distance between the antennas is far away; this requirement is difficult to implement from the perspective of engineering implementation. It is therefore recommended to use a combiner solution that satisfies the isolation.

After combining GSM1800 and F-band TD-LTE and sharing the sky surface with D-band, one can support two modes, three frequency bands, without considering the problem of antenna isolation during engineering implementation, and can achieve 1.8G and 2.6 at the same time. G independent ESC, independently optimized.

TD-LTE/GSM common station test results

The measured results of the single-station TD-LTE/GSM co-station based on the above scheme are shown in Figures 2 and 3. The eNB is in the red circle position in the figure, and the cell points in the direction of the blue arrow. The station is about 30 meters high.

It can be seen from Figure 2 that the coverage of GSM1800 remains stable before and after the co-station. Figure 3 shows the performance indicators of TD-LTE. For example, when the cell edge direction reaches 800 meters, the downlink rate is still greater than 10 Mbps (RSRP > -110 dBm). The above indicators are in full compliance with the expected results.

to sum up

In view of the problem of insufficient site resources in the domestic TD-LTE scale-up deployment, this paper proposes a TD-LTE/GSM co-site construction plan, and demonstrates its feasibility. It can be seen that the construction method based on GSM1800 has performance advantages over other joint station construction.

In the site solution, the scheme of sharing the antenna with GSM1800 is introduced. Due to the dual-frequency dual-emission antenna, GSM1800 and TD-LTE can achieve independent optimization of the electric downtilt angle.

In terms of TD-LTE/GSM coexistence, in order to meet the inter-system isolation requirements, it is recommended to use a combiner solution. Single station verification shows that the scheme guarantees the stability of the GSM1800 system, while the performance of TD-LTE has no significant loss. Further verification of the solution will be carried out for the next phase.