Vietnam Spectrum Occupancy Measurements and Analysis for Cognitive Radio Applications

Transcription

1 Vietnam Spectrum Occupancy Measurements and Analysis for Cognitive Radio Applications Vo Nguyen Quoc Bao Posts and Telecommunication Institute of Technology

2 Outline Introduction Measurement and Procedure Measurement Results and Analysis Conclusions

3 Introduction Radio frequency spectrum is a resource of fundamental importance in wireless communication systems. During recent years a multitude of wireless applications and services has been developed As a result, the need for new frequency bands increased.

4 Introduction Radio Spectrum Any wireless transmission occupies a portion of the radio spectrum. Only the licensed wireless agents are permitted to transmit on their allocated spectrum band. The current spectrum allocation Spectrum allocation is static. Allocation is almost reaching its limit saturation. The spectrum utilization-ratio is very low.

5 Introduction Military radio systems (19%) Public mobile radio (1%) Broadcasting (4%) Aeronautical (8%) Other (2%) Radar(24%) Fixed access (13%) Fixed wireless access & Satellite service (19%) Satellite mobile (5%) Land mobile (5%)

6 Introduction Recently, Cognitive Radio (CR) technology has become one of the most rapidly expanding research topics in the field of wireless communication. dynamically adapt to their environment and combine various information to achieve optimal performance. currently considered a promising solution for the problem of underutilization of spectrum. currently considered in some industrial standards: For example: P and IEEE Such technology is motivated by measurement campaigns comparing the spectrum regulations defined by governmental agencies and the actual usage by the licensees.

7 Introduction Several measurement campaigns concerning spectrum occupancy have been conducted world wide In USA (Chicago, New York) [McHenry, 2005] In Qatar [Qaraqe 2009] In Singapore [Islam 2008] In China (Guangdong) [Chen 2009] In New Zealand [Chiang 2007] In Spain [López-Benítez 2009] In Germany [Wellens 2007] A common finding among these studies is that spectrum is indeed heavily underutilized at the moment

8 Introduction Aim of Measurement To understand the current spectrum usage due to the fixed spectrum allocation in Vietnam and its utilization efficiency in Ho Chi Minh City and Long An province. To estimate the potential availability of spectral bands for Cognitive Radio. To create a first step on studying and designing cognitive radio wireless networks in Vietnam.

9 Measurement Locations: Site: the roof of the building owned by Radio Frequency Directorate (MIC), An Phu, District 2, Ho Chi Minh City Coordinate: 10 47'42.3; '25.9 Duration: Oct now Aerial map showing the measurement for measurement location (Courtesy of Google Inc.) North view

10 Measurement Locations Station: An Phu, District 2, Ho Chi Minh City Location: 10 47'42.3; '25.9" West view East view

11 Measurement Devices Antennas: HE016: active antenna system, omnidirectional reception of vertically and horizontally polarized signals 10 khz to 80 MHz (vertical) 600 khz to 40 MHz (horizontal) HE309: active vertical dipole, high sensitivity, large bandwidth and wide dynamic range from 20MHz to 1300 MHz. HE314A1: active omnidirectional antenna, reception of horizontally polarized waves from 20 MHz to 500 MHz. HF214: omnidirectional antenna, designed for the reception of horizontally polarized waves 500 MHz to 1300 MHz HF902: omnidirectional antenna designed for the reception of vertically and horizontally polarized waves from 1-3 GHz.

12 Measurement Devices Receiver: EM550, a fully digitized VHF/ UHF receiver, covers the frequency range 20 MHz to 3.6 GHz. Software: R&S ARGUS Monitoring Software

13 Measurement settings Sensing methods Energy Detector Feature Detector Matched filtering and coherent We choose energy detector Easy to implement Not require prior knowledge about primary signals. Energy threshold ITU recommendation [ITU Handbook Spectrum Monitoring, p. 168]: the threshold should be 10dB above the ambient noise. The theoretical ambient noise <> the actual ambient noise. In this work, we set the threshold 3 db above the minimum received signal power recorded in an observed band during 24h over 4 months.

14 Measurement results Remarks The level of background noise is a little higher than the theoretical ambient noise. The level of background noise is not constant and slightly increases with frequency resulting in an increase on the decision threshold. The actual spectrum usage pattern is not uniform, i.e, the spectrum below 1 GHz seems to be heavily utilized the spectrum from 2 to 3 GHz is found to be lightly used.

15 Measurement results

16 Measurement results

17 Measurement results Remarks This band is the most heavily utilized bands observed in this study. The typical maximum signal power of FM bands is from 0 dbm to -20 dbm. With TV channels, the maximum power is around -60dBm to - 40 dbm

18 Measurement results

19 Measurement results

20 Measurement results Remarks The other ones having a considerably higher occupancy rate compared with other type of frequency allocations. In the land mobile bands, MHz and MHz, it is easy to identify the spectrum of downlink GSM/E-GSM signals that are located in 950MHz and 1800MHz bands. The spectrum of downlink 3G/IMT2000 signals of four 3G service providers, i.e. Mobile, Viettel, EVN&HT, and Vinaphone, are observed ranging from 2110Mhz to 2200 MHz. The downlink channels in point-to-multipoint mobile applications are identified as mostly occupied, e.g. due to the active control channels constantly broadcasted by base stations to maintain cellular service coverage of GSM900, GSM1800 and WCDMA networks.

21 Measurement results Remarks Unlike downlink channels always transmitting with relatively high power, the usages in the uplink channels depend on the actual number of active mobile users in the measurement area and more intermittent according to their behaviors. We can see that as expected transmit power of GSM900 mobile stations is higher than that of GSM1800 mobile stations. We also observe that 3G uplink channels seem to be completely unused, e.g. due to the nature of WCDMA technology the transmit power of uplink channels in 3G system is very low, and might not be detectable by the measurement system.

22 Measurement results

23 Measurement results Remarks Most part of these bands band is unoccupied suggesting some opportunities for cognitive radio accesses. However, recalling that the whole band from 230 to 406 MHz is exclusively reserved for security services and systems of the Vietnam ministry of public security (MPS). should be precluded by secondary access

24 Measurement results Remarks: The ISM band is considered as the most open band, i.e. many wireless applications are operated including WiFi transmitters, cordless telephones, microwave ovens, and various consumer products This band appears to be unoccupied. It can be explained by the fact that this frequency band is usually occupied in indoor environments and signals at such frequencies are severely attenuated by walls.

25 Measurement results The rest of spectrum between 2.4 GHz and 3 GHz mostly unused, with the exception of some signals with very low duty cycle in bands allocated to aeronautical and satellite radiolocation and radionavigation, ( and MHz), DECT cordless phones ( MHz) and military radars ( MHz).

26 Measurement results Ho Chi Minh City

27 Measurement results

28 Measurement results Remarks Some spectrum bands are subjected to exhaustive usage while some others are sparsely used or show temperate utilization, and, in some cases, are not used at all. In general, the average spectrum occupancy observed in Ho Chi Minh City is 13.74% for the whole frequency range between 20MHz and 3000 MHz and the band assigned for television broadcasting is the highest occupancy band with 58%. Stated another way, 86.25% of this spectrum is unused. The obtained results demonstrate that Ho Chi Minh City spectrum utilization exceeds Long An by roughly 1.46%, which, in turns, exceeds New Yorks by 1.15%.

29 Future Work A part of a larger on-going measurement campaign conducted by PTIT in several cities in the south of Vietnam. The purpose of this project is to create a usage map for cognitive applications. Our measurement results suggest that in Vietnam Most of allocated frequencies are underutilized except for mobile and broadcasting bands CR applications can be realized by exploiting bands with low measured occupancy rates. However, care must be taken to account for possible wireless channel effects such as multi-path and hidden terminal problems.

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