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NSMA Conference

NSMA Conference. Interference Temperature Round Table May 18, 2004. Les Wilding Cingular Wireless 5565 Glenridge Connector Atlanta, GA 30342. Topics for Discussion. 1. Interference Temperature as it Applies to Point-to- Point Microwave Links.

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NSMA Conference

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  1. NSMA Conference Interference Temperature Round Table May 18, 2004 Les Wilding Cingular Wireless 5565 Glenridge Connector Atlanta, GA 30342

  2. Topics for Discussion 1. Interference Temperature as it Applies to Point-to- Point Microwave Links. 2. Interference Temperature as it Applies to CMRS Networks. 3. Summary

  3. Interference Temperature and Point-to-Point MW • In the NPRM section the Commission discusses applying the • interference temperature concepts to both the FSS and FS services. • Band Segments selected by the Commission for deployment of • unlicensed devices are: • FSS Band Segment 12.75 - 13.25 GHz • (excluding 13.15-13.2125 GHz) • F S Band Segment 6525 MHz to 6700 MHz • Note: In the FS category the Commission selected the lower half • of the full (6525-6875 GHz) upper 6 GHz band.

  4. Interference Temperature and the Digital MW Link Commission Assumption 1: 126 dB margin When computing interference, the interfering path (path C to B) must be below the interference objective for the victim microwave link (path A to B). Figure 1

  5. Interference Temperature and Point-to-Point MW • Coordination objectives for interference are based on published T/I • curves for the victim receiver and the interfering carrier. • The Interference objective for coordinating a typical MW link is: • I (Coordination) = – 75.5 dBm – 34 dB – 5 dB = – 114.5 dBm • Where: 75.5 dBm = the Static BER Threshold of 10-6 • 34 dBm = the Specific T/I threshold for the victim and • interfering bandwidths and frequency offsets. • 5 dBm = Multiple Exposure Allowance • The unfaded C/I (Coordination) for a digital link is: • {-40 dBm- (-114.5 dBm)} = 74.5 dB

  6. Interference Temperature and the Digital MW Link The NPRM describes an unlicensed device that is transmitting on 6600 MHz with an output of -41.25 dBm/MHz and operating 100 meters from a FS receiver with a discrimination angle of 20 degrees. The formula for calculating the operating margin is; EIRP (A) - Path loss (A to B) - C/I (Coordination) => EIRP (C) - Path loss (C to B) + Disc Loss (B to C) Using the coordination data for the MW path and correcting the EIRP of the unlicensed device for 3.75 MHz bandwidth yields: 64 dBm-140 dB-74 dB => -35.5 dBm -93 dB - 43 dB which = -150 dBm > -171.5 dBm : = 21.5 dB margin This is the margin for ALL interferers not the 126 dB in the NPRM

  7. Interference Temperature and the Digital MW Link Commission Assumption 2: Use of Transmit Power Control TPC Use of Dynamic Freq. Selection DFS Figure 2

  8. Interference Temperature and the Digital MW Link • For this to work, the TPC and DFS detectors in unlicensed device • would have to hear the MW signal from site A and make decisions • about what is happening at site B in order to set its transmit level. • The propagation path (A to C) is primarily along the ground and not • subject to atmospheric disturbances. Whereas the FS link (A to B) is • subject to atmospheric disturbances. • This could lead to a situation where there is a lot of fading activity on • path (A to B) that is not seen by the ground based unlicensed receiver • thus causing false decisions and cases of interference into site B.

  9. Interference Temperature and the CMRS Network • CMRS networks already manage interference in real time • Transmitter Power Control • Frequency hopping & modulation coding techniques • CMRS operators have greatly reduced self-interference • Improved capacity and higher data throughput • Increased cell coverage uses total radio channel sensitivity • Unlicensed Devices are incompatible with CMRS networks • CMRS operator can not control external interference • External interference raises noise floor, • Lowers system capacity • Lowers system/customer data throughput • Increases mobile transmit power/lowers battery life • Lowers quality of service

  10. Interference Temperature • Summary: • Interference Temperature is a CONCEPT • It needs to be adequately defined and quantified before it • has any value in spectrum management. • SDR and Cognative Radios are in their infancy and are not ready • to take on the tasks envisioned by the Commission. • Most users of licensed spectrum make use of the total range of • receive levels down to and including the thermal noise floor of • their communications systems. • FS and FSS licensed services can not tolerate interference levels • greater than the currently authorized Part 15 levels.

  11. Interference Temperature In short, I commend the Commission for thinking outside the box BUT the Commission has put the licensees feet into the water before the ARK has been built to protect the licensed users from drowning in a sea of interference.

  12. Interference Temperature and Point-to-Point MW The Digital Microwave Link • Digital microwave paths are designed to meet a desired performance • measured in: • Error free seconds. • Unavailability in seconds per year. • The components that make up this performance are: • Its composite fade margin (CFM). • Its threshold to interference (T/I) margin. • The link’s CFM is primarily the sum of the flat (thermal) and • dispersive fade margins.

  13. Interference Temperature and Point-to-Point MW The Digital Microwave Link Figure 1

  14. Interference Temperature and the Digital MW Link Commission Assumption 1. 126 dB of margin and S/I Requirement of 30 to 50 dB • Equipment used in a typical MW link • The NEC 2600 series MW is typical of the radios used in this band • Transmitter output power + 28.5 dBm max • Modulation = 128 QAM • Modulation bandwidth = 3.75 MHz • Receiver threshold BER of 10-6 = -75.5 dBm • T/I Co-channel = 34 dB • T/I adjacent channel = -5 dB • Receiver outage threshold BER of 10-3 = -78.5 dBm • (assumed to be 3 dB worse than the static threshold) • The Andrew PAR6-65 antenna is a typical Category A antenna

  15. Interference Temperature and the Digital MW Link Commission Assumption 1. 126 dB of margin and S/I Requirement of 30 to 50 dB Coordination of a typical MW link Microwave transmitter output power: + 28.5 dBm Typical losses on the transmit side: - 3.0 dB Typical gain for a 6 foot MW dish: + 38.8 dBi Typical EIRP: = + 64.3 dBm The unfaded receive signal level for a typical 40 km path is: + 64.3 dBm -140 dB (path loss) +38.8 dBi - 3 dB (feeder) = -39.9 dBm In the digital world, EIRP’s range from 60 dBm to 75 dBm based on a typical 0.5 watt to 2 watt transmitter and a 6 to 8 foot diameter standard performance dish.

  16. Interference Temperature and the Digital MW Link Figure 3

  17. The FCC’s Definition of Interference Temperature • Originally proposed by the Spectrum Policy Task Force (SPTF) • as an “Interference Management Concept” to: • Establish a maximum level of interference that can be • tolerated by a receiver but ONLY after a systematic and • thorough study of the existing RF environment. • Establish a clear definition of the spectrum users Rights • and Responsibilities • Establish a clear quantifiable definition of Harmful Interference

  18. The FCC’s Definition of Interference Temperature The FCC’s Interference Temperature Metric as defined in ET Document 03-237 is: A measure of the RF power generated by undesired emitters plus noise sources that are present in a receiver system (I+N) per unit of bandwidth. More specifically, it is the temperature equivalent of this power measured in units of Kelvin. There is no basis for the term or a definition of “Interference Temperature” in any of the Standards documents. The Commission used the cookbook approach by taking parts of the definitions of Antenna Temperature and System Noise Temperature to cook up their Interference Temperature dish.

  19. The FCC’s Concept of Interference Control • The Commission would have you believe that a licensee would • be agreeable to accepting some guaranteed maximum level of • interference (Interference Temperature Limit) • To accomplish this the FCC is proposing to employ one or more • of the following techniques: • Use of Software Defined Radios to select frequencies and/or • modulation modes that would avoid interference. • Use of Cognitive Radio technologies (smart radios). • Deployment of remote monitoring receivers to sense the • RF environment. • Incorporation of RF interference monitoring technology into • the licensed receiver to detect the presence of interfering • signal levels.

  20. The FCC’s Concept of Interference Control • Deployment of a grid of monitoring stations that would sense • the interference temperature and broadcast this data to all • unlicensed devices. • Problems with the monitoring scenarios • These approaches, with the exception of equipping the licensed • receiver with a monitor, all fail to accurately identify the • interference conditions as seen by the victim licensed receiver. • They all require spectrum for communications with/between the • monitoring device(s) and the unlicensed devices.

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