1 LTE and WiFi network technology characteristics analysis
As the preferred mobile communication system for next-generation networks, LTE has some unique technologies. Compared with WiFi network technology, LTE has the most advantage of being able to achieve the same-frequency networking through ICIC (Inter-Cell Interference Coordination) technology.
ICIC mainly controls inter-cell interference by managing radio resources, and is a multi-cell radio resource management considering resource usage and load in a plurality of cells. Specifically, the ICIC limits the use of radio resources in each cell in an inter-cell coordinated manner, including limiting the use of time-frequency resources or limiting its transmit power on certain time-frequency resources.
The LTE Rel-8 version first supports the ICIC mechanism. The base station can exchange RNTP (related narrowband transmission power), HII (high interference indication) and OI (overload indication) signals through the X2 interface to implement intra-carrier frequency domain data channel inter-cell. Interference coordination. The original Rel-8 version focuses on the application scenarios of heterogeneous networking of macro base stations. The Rel-10 version proposes eICIC (Enhanced Inter-Cell Interference Coordination Mechanism) to support strong interference scenarios (such as macro stations and micro stations, macro stations and Home base station, etc.) The case of heterogeneous networking. The Rel-l1 version, which is currently in the research stage, proposes the FeICIC (Further-eICIC) work item to address the legacy issues in eICIC and further study other inter-cell interference coordination technical solutions.
The eICIC proposed in the Rel-10 version can be roughly divided into three categories: time domain interference coordination, frequency domain interference coordination, and power control.
1) Power control scheme
When the serving cell and the neighboring cell use the same frequency resource, the solution may appropriately reduce the transmit power of the serving cell or the neighboring cell to improve the performance of the interfered macro base station user. Compared with the traditional closed-loop power control scheme, power control is from the perspective of suppressing inter-cell interference and optimizing the overall cell edge performance of the system until a desired SNR (Signal to Noise Ratio) value is reached.
As an important ICIC solution, the power control scheme has been widely used in heterogeneous networks, such as macro and Pico (pico cell), macro and home base stations and other heterogeneous scenarios. This scheme can be used for backward compatibility of the system, and is applicable to both FDD (Frequency Division Duplex) and TDD (Time Division Duplex) duplex modes. However, the implementation of the power control scheme must be based on the user's measurement and reporting, and the design and interaction of the interaction information between the base stations needs to be considered.
2) Frequency domain scheme
The realization of ICIC in the frequency domain is actually the scheduling of resource constraints, that is, different cell signals are scheduled in the frequency band, and OFDM (Orthogonal Frequency Division Multiplexing) narrow-band orthogonality is used to realize orthogonal transmission of signals, thereby achieving interference cancellation. The frequency domain interference coordination scheme can well solve the backward compatibility problem of the terminal in the Rel-8/9 version, and is also applicable to the FDD and TDD duplex modes. However, the implementation of the solution is also based on user measurement and reporting and inter-base station information interaction, which increases the overhead of backhaul signaling and the detection complexity of the macro station.
3) Time domain solution
The Rel-10 version focuses on the time domain interference coordination scheme. The scheme schedules the interfered users on time-domain resources such as subframes or OFDM symbols. These time-domain resources have been reduced in various other ways. Interference at other nodes.
2 LTE and WiFi network coverage capabilities analysis
Through the comparative analysis of the existing wireless coverage capabilities of LTE and WiFi, the advantages and disadvantages of the two in terms of coverage capabilities are listed, and the coverage scenarios suitable for the two networks are analyzed.
2.1 LTE coverage capability
Since the coverage capability of LTE is closely related to the standard and frequency bands, we use the FDD-LTE standard that telecom may adopt to measure the coverage radius.
Select 2.1 GHz FDD-LTE, 2 & TImes; 15 MHz bandwidth, cell edge rate 4 Mbps / 256 kbps, base station side antenna configuration 2 & TImes; 2 MIMO, wireless propagation model is standard COST231 HATA.
The specific link budget is shown in Table 1.
The FDD-LTE dense urban site has a coverage radius of 320 m and a station spacing of 480 m; the general urban site has a coverage radius of 440 m and a station spacing of 660 m.
2.2 WiFi coverage capability
At present, there are three main methods for WiFi network coverage: direct coverage of indoor APs (access points), coverage of indoor AP combined systems, and direct coverage of outdoor APs. AP equipment types mainly include outdoor 500 mW, indoor 500 mW and indoor 100 mW. Indoor 100 mW is used for indoor direct coverage, indoor 500 mW is used for indoor distribution system coverage, and outdoor 500 mW is used. Cover indoor or outdoor areas.
1) Link loss
a) WLAN (wireless LAN) in 2.4
The COST231-Hata wireless propagation model is generally applied in the 5 GHz band: transmission loss Lp = 46.3 + 33.9 lgf - 13.82 lghb + (44.9 - 6.55 lghb) lgd.
Where d is the distance between the base station and the terminal, hb: the height of the base station antenna, and f: the carrier frequency.
b) The uplink budget formula (ie calculating the maximum allowed Lp for the uplink):
Indoor Lp = terminal transmit power + terminal antenna gain + AP antenna gain - AP receive sensitivity - shadow reserve - penetration loss
c) Downlink budget formula (ie calculating the maximum allowable Lp for the downlink):
Indoor Lp = AP Transmit Power + AP Antenna Gain + Terminal Antenna Gain - Terminal Receive Sensitivity - Shadow Reserve - Penetration Loss
d) The empirical values ​​of 2.4 GHz electromagnetic waves for various penetration losses are as follows: barrier of partition wall (wall thickness 100-300 mm): 20-40 dB; floor barrier: 30 dB or more; wooden furniture, doors and other planks Blocking of the partition wall: 2
15 dB; thick glass (12 mm): 10 dB; ordinary glass window (3 to 5 mm): 5 to 7 dB.
Table 1 link budget table
2) Indoor placement type AP coverage capability
Since the indoor 100mW AP and the user are on the same floor, the AP antenna height is considered to be 3m; since the indoor 100mW AP covers only a small area on the same floor, the shadow reserve is not considered.
The design specifications of China Telecom operators stipulate that: 95% of the locations in the target coverage area, the received signal level is not less than -75dBm, that is, the receiver sensitivity of the self-contained network card is -75 dBm. Since the data service has asymmetric characteristics, Therefore, the uplink rate is not high. The sensitivity of the AP receiver is -79 dBm, and the sensitivity of the self-contained NIC receiver is -75 dBm. The specific coverage is shown in Table 2.
In the actual engineering planning and design, the indoor open space coverage distance is generally 40 m, and the indoor partition wall coverage distance is generally 15 m.
3) Indoor distributed AP coverage capability
The propagation model of the indoor antenna to the user terminal can be referred to Table 2. The antenna output power (EIRP) requirements on the corridor are: 10 dBm ≤ EIRP ≤ 15 dBm, and the distance between the antenna and the antenna is strictly required to be 10 to 15 m; Antenna output power (EIRP) requirements for coverage of the room: EIRP ≥ 8 dBm, which can be less than the power of the antenna output on the corridor, and the distance between the antenna and the antenna can be relaxed to 20 to 25 m.
4) Outdoor AP coverage capability
The outdoor AP is directly covered, and a high-gain antenna is generally used. The antenna is installed in a high area and can directly view the entire coverage area. More than 95% of the target coverage area, the received signal level is -75dBm, and the AP receiver sensitivity is -77 dBm. The specific coverage is shown in Table 3.
In actual engineering planning and design, the outdoor open space coverage distance is generally 250 m, and the indoor coverage distance is generally 80 m.
2.3 LTE and WiFi coverage capabilities
From the above analysis, LTE has better coverage than WiFi, and mobility support is much higher than WiFi. In indoor scenarios, LTE uses 2.1 GHz band or 2.3 GHz band, and coverage is better than WiFi. 2.4 GHz is lower, and antennas and devices gain more, so LTE has better coverage than WiFi in indoors.
In summary, LTE is far superior to WiFi network in coverage capability. 3 LTE and WiFi network wireless capacity analysis
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