i''1,;-",

IEEE Vehicular Technology Conference (VTC), Ottawa, Canada, to be published September 2010.

Analysis and Simulation of Adjacent Service Interference to Vehicle-Equipped Satellite Digital Receivers From Cellular Mobile Terminals

Theodore S. Rappaport Stefano DiPierro, Riza Akturan Networking and Communications Group Sirius XM Inc. The University of Texas at Austin [email protected] Austin, TX, USA [email protected] [email protected]

Abstract- This paper provides detailed analysis and simulation recommendations for the WCS-SDARS adjacent channel for explol'ing the impact of out-of-band emissions (OOBE) of problem. adjacent wireless services to the Sirius XM digital satellite radio service. Based on an extensive analysis of interference from II. THE SIRIUS XM SATELLITE BROADCAST SYSTEM (SOARS) vehicles with mobile cellular users in realistic roadway conditions, we propose proper methods for determining out of ANDWCS band emission spectral masks that should be used by new WCS The Sirius XM satellite radio system is a broadcast system cellular subscriber transmitters. in the 2.3 GHz band. Analysis for designed for simplex transmissions (receive-only) [1]. The roadway and propagation conditions in various US cities resulted inability to use feedback for stations in turn in the suggested masks. This work presents the first simulation of requires them to have more protection from interference than its ldnd and offers approaches that federal regulators may use to other systems that are dynamically adjustable. Broadcasters determine spectral masks that allow harmonious co-existence of existing mobile radio listeners with new cellular and fixed are licensed based upon their fixed installation and placement broadband mobile services in adjacent spectrum bands. of transmitters, and are given strict licensing requirements with their spectrum allocation. Because of the fixed and rigid Index Terms- cellular, interference, mobile, radio, satellite, requirements of transmitter power levels, antenna heights, and simulation placements, broadcast systems are operated in a "noise­ limited" regime, where the coverage provided by the I. INTRODUCTION broadcaster is limited by the signal power it is able to Wireless Communications Services (WCS), a fixed and propagate to the listener, and the listener's noise level at her mobile cellular service, has been allocated spectrum adjacent to receiver. Cellular systems, on the other hand, are operated in a the US satellite radio service (SDARS). Figure 1 noise-limited regime, and are relatively unrestricted by their shows the spectrum allocations for SDARS and WCS systems. license from adding new base stations and adding more Sirius and XM were merged in 2008 to create Sirius XM subscribers over time within a geogl'aphic area, as customers Satellite Radio, which uses the SDARS spectrum and has over are added to the network. Broadcast systems are designed to 20 million satellite receivers installed in the US that currently maximize coverage from just one or· a few transmitters, listen between 2320 MHz and 2345 MHz. WCS is assigned although may be used to augment coverage spectrum in the 2305-2320 MHZ band and the 2345-2360 MHz bands, and wireless carriers are in the early stages of rolling out problems. For Sirius XM, hundreds of ground based repeaters commercial service. Part 27 of the FCC rules regulate the are located throughout the US to provide coverage holes adjacent service interference from WCS to SDARS services. caused by shadowing of the satellite signal due to buildings and foliage, although repeaters cover less than 1% of the To date, the literature has not offered a careful study of CONUS coverage region. Achieving high broadcast quality of interference that mobile cellular terminals have on mobile service targets required the use of dual path satellite diversity satellite receivers since such mobile cellular services are new broadcasting, and antenna beam shaping to increase the link and have only been available the past few years. Federal margin in areas with lower elevation angles to the satellites. communications regulatory agencies such as the FCC must have ways to analyze the impact of adjacent channel Since broadcast systems use one-way transmission interference between such diverse systems as satellite radio systetrts, they do not introduce additional interference as broadcasting and cellular voice and data networks. This paper provides a detailed analysis that may be used for determining listeners are added. This is because all new listeners are the impact of cellular-like interference on receive-only satellite simply receive-only - they do not transmit, and thus do not broadcast systems, and provides specific spectral mask add to the spectral interference level of the system. The fact that broadcast systems do not produce interference as listeners are added is in contrast to wireless mobile systems which Sponsored by Sirius XM Satellite Radio Inc. continually increase their total interference power levels and intermodulation products from nearby WCS mobile out of band emissions (OOBE) as more mobile subscribers are transmitters that overtake the receiver circuitry at satellite added to the network. Degradation of the link margin due to radio receivers. The only way to fully understand the impact OOBE interference implies that there is less excess power on and sensitivities of communication system performance is the radio link to protect against fading and interference. In the through complex Monte Carlo simulation, as described in the event that the fading or interference losses exceed the link following. margin, the receiver's reception will fail. III. A SIMULATOR FOR STUDYING WCS OUT-OF-BAND techniques of the Sirius XM satellites, types of INTERFERENCE IMPACT ON SOARS satellites used, apportionment of content on the satellite To determine realistic interference levels and the resulting uplinks, and use of redundancy are slightly different in the degradation to satellite receivers, we developed an extensive legacy XM and Sirius systems, yet both systems provide simulation environment based on Matlab. The simulator allows extremely similar signal level performance on earth, as both an engineer to input important propagation parameters, traffic satellite systems were designed and deployed using state-of­ parameters, and transmitter and receiver parameters to the art satellite engineering concepts under similar FCC rules determine real-world affects and resulting SDARS outages [I]. SDARS is a mobile service that requires an omni­ caused by WCS mobile stations that radiate out-of-band directional reception capability on a vehicle installation. interference. The use of simulation is arguably the only method Satellite signal power levels are weak when compared to for determining the impact of OOBE on the listening public in realistic environments. The simulator considers the random modern terrestrial mobile and fixed wireless systems. For location of WCS mobile stations and SDARS listeners, the example, the Sirius satellite power level received in Miami is - likelihood of whether the WCS mobile stations are transmitting 101 dBm, and the thermal noise level is -113 dBm/ 4 MHz, and if the SDARS receivers are turned on, the duty cycle of a yielding 12 dB signal to noise ratio without WCS interferers. transmitting WCS subscriber, whether the WCS subscribers are fi·om the different WCS spectrum blocks, whether the WCS The WCS system is not yet deployed, but will most likely system is using mobile station power control, and the particular be a cellular-like broadband wireless system to provide mobile transmission power and power control level for each and fixed broadband service using a cellular architecture. transmitting WCS subscriber station. The simulator also allows While the Sirius XM broadcast system provides signal levels the user to specify different vehicl~-to-vehicle path loss models that are no greater than -94 or -95 dBm over a 4 MHz that govern the propagation of out-of-band interference fi·om on earth, cellular systems typically operate at the WCS mobile stations to each of the Sirius XM receivers, minimum useable signal levels of -80 dBm or greater over a 4 and different user-specified masks, are used on each of the MHz bandwidth, certainly with much higher link margins than WCS mobile transmitters. This allows us to compare of the satellite systems, as they are pre-designed to anticipate future impact of WCS OOBE on SDARS listeners. The simulator self-interference fi·om more users over time. Typically, also uses the satellite look-angle data and link margin data to cellular systems operate at 20dB to 30 dB above the thermal determine accurate outage probabilities for a wide range of noise floor, and use adaptive modulation on both the forward different latitudes and . and reverse link for agility in signaling data rates to adapt to changing interference and coverage levels. IV. HIGHWAY TRAFFIC, ROADWAY, AND SUBSCRIBER ADOPTION RATE MODELS Regardless of the size of the guard band between the The simulator must properly model the impact of adjacent SDARS spectrum and the WCS emissions, it is the power service out-of-band interference from mobile WCS users, and level of out-of-band-interference allowed to come from WCS the resulting degradation to mobile SDARS listeners, thus it is subscriber units that will dictate the level of degradation to the necessary to first consider a realistic highway environment. SDARS listener. The current FCC rules call for an OOBE Our simulator allows the engineer to enter roadway length (in mask defined by 11 0+ 1OlogP for mobile transmitters. The miles), the number of highway lanes on the road, the average OOBE formula requires that the WCS subscriber out-of-band speed of each vehicle, and the traffic volume of vehicular emissions within the 1st MHz of the SDARS band directly traffic as measured in cars per hour. Our simulator then adjacent to the upper or lower WCS blocks shall not exceed - generates the random locations of specific vehicles traveling 110 dBW per MHz. These FCC rules were based on the throughout a highway. We assume interstate highways and requirement that WCS protect SDARS such that any out of freeways have lane widths of 3.5 meters in the simulation, band interference would only be allowed to raise the SDARS which is standard for roadway construction. noise floor by 1 dB. In the simulation, we assume that each lane of has a uniform distribution of highway traffic, so that users may be The WCS transmitters also have the ability to overload the randomly located in any of the highway lanes, as found in SDARS receivers, such that there are two independent typical ·urban and suburban highways. The selection of mechanisms from the adjacent band WCS transmitters - roadway length is a variable parameter and can be adjusted to OOBE that creates a linear increase in the noise floor due, and describe the roadway being modeled. For the simulations, we desensitization due to non-linear signal overload and chose five typical US cities with varying latitudes and ,-, '\~

longitudes (New York City, Jackson, MS, Denver, CO, Old, and WCS New, we propose several different vehicle-to­ Miami, FL and Charlotte, NC), and selected popular highways vehicle propagation path loss models [8], [9]. [10]. We employ within each of those cities where Sirius XM relies upon the concept of a mean attenuation factor, a diffraction satellite coverage, and not its terrestrial repeaters. Each of the parameter that models the cumulative effects of car body loss, selected road segments has a corresponding daily traffic human body loss, and blockage between vehicles. Based on volume (in cars per day) distributed over a 24 hour period. reported measurements, we assume loss factors of 10 dB and For the simulator, we assume that 60% of the daily traffic flow 16 dB, and consider path loss exponents of n=2.0 and 2. I 8. occurs during the 4 peak hours (two peak morning hours of 7 - We also assume log-normal shadowing due to variations in the 9 am and two peak evening hom·s of 4 -6 pm) during a day, channel, and consider standard deviations of the shadowing to and determine a typical rush hour traffic volume (in cars per be 0 dB, 2 dB, and 4 dB. We note that the loss factors add hour) by multiplying the overall daily volume by 60%, and attenuation above the distant-dependent path loss model, and then dividing by 4. the log-normal shadowing allows our simulator to generate realistic random effects that will impact interference levels At any given time during any one of the foUl' peak travel received at SDARS receivers. We use Xcr to repr•esent a hours, the gross number of vehicles is determined by random shadowing loss that is assigned a mean value of either multiplying the traffic volume by the roadway length, and then 10 dB or· 16 dB, and is log-normally distributed (normal in dividing by the speed of travel. The total number of vehicles dB), and the free space loss at 1 m is 40 dB. In our on the roadway segment, a certain proportion will be satellite simulations, Xcr is a Gaussian random variable having values radio subscribers and another portion will be WCS service in dB. The simulator allows the user to consider either a free subscribers. The simulator provides inputs to specify the user space path loss exponent value of n =2.0, as well as a path loss density of SDARS listeners and WCS users. These data are exponent value of n = 2.18. Standard deviations for the log­ entered as a customer penetration rate, in terms of percentage normal shadowing component are selected as either 0 dB, 2 of total vehicles, and dictates the user density of both WCS dB, or 4 dB for the path loss. users and SDARS listeners on the simulated highway. For the work presented here, a satellite radio penetration rate of 34% is The simulation applies the path loss model to the all of used. WCS market penetration was estimated to be a WCS transmitters and generates a random path loss value for moderate 5%. It is assumed that only half of those WCS every WCS transmitter. Then, the simulator computes the transmitters interfere with one of the satellite radio systems, distance between every WCS vehicle and SDARS vehicles, and their OOBE is adjusted properly to account for their and computes the resulting received interference power at each frequency separation from the satellite radio band. Also, SDARS receiver, based on the particular FCC interference random duty cycle assignment is made on the WCS protection mask that is specified in the simulator. We make transmitters, and as a result, their OOBE was scaled to account the fair assumption that each WCS transmitter is independent for their duty cycle and the power control. Vehicle-to-vehicle from one another, or at least uncorrelated and of zero mean, signal propagation was modeled using publicly available such that the interference powers from multiple WCS measUI'ement data. Based on published papers from the transmitters are added in a linear fashion at a particular Netherlands, Carnegie Mellon University, and the Intelligent SDARS receiver. Based upon the simulated levels of Vehicle Highway Systems community, we find that many interference at each SDARS receiver over a large number of measurements and models have been proposed for vehicle-to­ iterations, the simulator produces statistics that determine vehicle communication systems in the 900 MHz to 6 GHz SDARS listener quality degradation based on outages, as well range [2], [3], [4], [5], [6], [7]. These models in the literature, as the satellite link margin reduction due to WCS interference. and the models used in the simulation, follow the form given by eqn. 4.69a in Rappaport's 2002 Wireless Communications For the simulation results presented here, we assume that text as active WCS transmitters are proportioned such that 64% of the WCS transmitters are transmitting with full subscriber PL (dB)= [Free Space Loss at 1m]+ 10*n log (d)+ Xcr (1) transmit power levels, 23% of the WCS transmitters are transmitting at 6 dB below their maximum power level, and where n is the path lost exponent and Xa is a mean diffraction 13% of the WCS transmitters are transmitting at 12 dB below loss parameter and Gaussian distributed in dB. Carnegie their maximum power level. The step of implementing the Mellon proposed a path loss model having a log-distance path effect of power control is performed on the eligible loss exponent of n=1.8, and a log-normal shadowing of 5.5 transmitters that remain, after "turning off' the transmitters dB. Other propagation models propose a free space path loss that are inactive based on the specified activity factor. model of n=1.8 to n= 2.0, and one study found that n=3.1 but indicated the high value of n is likely due to a single The simulator allows for the user to specify attenuation attenuation factor related to car body loss. values that are applied to the WCS transmitter spectrum masks, in order to take into account the FCC's proposed rules Based on the above cited data, as well as measured results that require WCS interference components at SDARS provided by Sirius XM and WCS operators in SWRI, WCS receivers to produce less interference as the frequency separation increases. The model used in the simulator allows 12 dB from full power. All the WCS transmitters, active and the user to select different levels of attenuation to be applied to inactive, then receive a random power level assignment for the WCS transmitters at different frequencies away from the each iteration. SDARS spectrum. The received power at the SDARS receiver is calculated For example, to study the FCC's proposed rules, the by subtracting the total path loss, per the vehicle-to-vehicle simulator must implement the 55+ 10logP spectral mask for a propagation models in Section 4 from the transmitted power. 0.25W WCS subscriber transmitter using a 2.5 MHz channel Included in the total path loss is the statistical blockage factor in the D block. To do this, we compute the attenuation with a settable mean level in dB, and a standar·d deviation required by the mobile station as 55 + 10log(0.25W) dB. This settable to between 0-4 dB. The mean for the blockage is equates to 55 db- 6 dB,= 49 dB of a.ttenuation applied to all assumed to be a minimum of 10 dB, and maximum 16 dB. D block WCS transmitters. For all WCS transmitters assigned This factor is randomly assigned for each individual to be in the first adjacent channel (e.g. the A-upper block), the calculation. The engineer can vary the path loss parametet·s to simulator implements 61 - 6, or 55 dB of attenuation level to assess performance using different assumptions. implement the FCC's proposed 61 + lOlogP OOBE mask for Traffic volume, speed and roadway characteristics the case of 0.25W transmitters. The simulator applies 67 - 6 = determine the total number of vehicles on the simulated 61 dB of attenuation for the B-upper block WCS transmitters roadway segment at any time during the peak rush hour. A in order to implement the FCC's proposed 67 + 10logP mask subset of the total vehicles will be satellite radio subscribers or with 0.25 W transmitters. If all WCS carriers use subscriber WCS service subscribers. The number of subscribers to both equipment that have identical spectral mask characteristics, services depends on how widely consumers adopt the then it is reasonable to assume that identical equipment in the respective services. This adoption factor is referred to as the WCS upper band (A block) would cause less interference into penetration rate. For the satellite radio, it is likely that the the SDARS band as compared to D block transmitters, since penetration rate will grow to 34% of vehicles in the next few the spectral emissions from WCS subscribers are further years. The WCS penetration rate is more difficult to estimate attenuated. as there is little or no current service available. Therefore a penetration rate of 5% was assumed for the simulations. As discussed earlier, the simulator computes the distances Penetration rates for both services are settable parameters in between all WCS and SDARS vehicles, and then calculates the the model, and can be adjusted for future growth. As both random path loss for WCS signals at each SDARS receiver services grow, the likelihood of their subscribers sharing the based on a distant-dependent path loss model with a mean road in close proximity will increase. The final step in diffraction parameter. The cumulative interference at each conducting this analysis is to evaluate the impact of SDARS satellite receiver is then calculated by summing up interference received at the satellite radio in terms of link interference levels from all WCS transmitters. For each quality and signal availability. iteration, the simulator computes and stores the aggregate power from each of the WCS transmitters as seen at each This relationship between link margin and elevation angle SDARS receiver, as well· as the aggregate total WCS OOB can be statistically estimated using a technique called the power which appears as interference. The overall statistics of WCS interference power levels are computed over many EERS model [11]. This model computes the outage iterations. The simulator uses the satellite look angles, antenna probability for different combinations of elevation angle and patterns, and link margins in order to determine the signal link margin. This produces a quality of service level to levels at different locations on earth. The simulator compare performance with and without interference. incorporates the actual designs employed by Sirius XM to Similarly, we also find the number of satellite radio users that exceed 99% availability under worst case Extended Empirical experience link margin degradations that exceed of 1, 2 or 3dB Roadside Shadowing (EERS) model assumptions [11]. or more.

V. SIMULATION RESULTS We ran simulations for five major US cities: Charlotte, NC, Miami, FL, New York/NJ Tumpike, Jackson, MS and As described in Section 4, the power control "bands" used Denver, CO. As example, we simulated rush hour traffic on a in the simulation are based on a statistical distribution of WCS 7.5 mile portion of Highway 836, southwest of Miami FL. vehicle location in a base station coverage area. The power Table 1 shows the traffic parameters for Miami which were control levels are settable and distributed randomly to the applied to the simulator. Using the traffic volume calculation WCS users, in propmiion to the cellular coverage zones, and techniques, we calculate a peak hourly volume of 13795 the simulations have been set to 0 dB (max power), -6 dB, and vehicles on the highway. Using the simulator, with the satellite -12 dB from full power. Out of the total pool of WCS link parameters shown in Table 2, we found that the Baseline transmitters on the roadway segment, a pmiion is declared availability is 99.78% for a 99% worst case availability inactive due to the WCS activity factor of only 13% being on. critel'ion. In other words, without WCS interference, only Specifically for the results presented here, the WCS users are 0.22% of the SDARS receivers in the Miami will experience assigned power control values in the following way: 63.2% at an outage more than 1% of the time. full power, 23.4% backed off by 6 dB, and 13.4% backed off TABLE I. TRAFFIC PROFILE It can be seen that the FCC mask would allow 10.66% and Parameter Value 3.71% ofthe SDARS receivers in Miami, respectively, to dip Location HWY 836 West of Miami below the current design specification of 99% availability, and Road Type Freeway 10.66% and 3.71% of the SDARS receivers, respectively, Peak Traffic Time Mondays, 5:15PM would suffer link margin degradation by 3 dB or more for Road Segment Length 7.5 Miles Average Speed 25 miles/hour various vehicle-to-vehicle propagation models. Number of Lanes 3 Average Daily Volume 91969 We note that in heavily populated cities such as Charlotte, Miami, and NYC/NJ, the proposed FCC mask would cause TABLE II. SATELLITE PARAMETERS AND BASELINE QOS 4.95%, 10.66%, and 7.72% of the SDARS listeners to dip below the 99% worst case availability design threshold. With a higher Joss propagation model between vehicles, the same cities have 1.88%, 3.71% and 3.06% of the listeners breach the 99% availability design goal. When considering the A total of 7,251,200 vehicle locations were simulated percentage of listeners that suffer more than a 3 dB drop in over 100 iterations, where each iteration was conducted under link based on WCS interference, we see that 5.24%, 10.66%, the assumption that 103 WCS transmitters and 704 SDARS and 6.23% of the receivers in the above named cities are receivers were located nearby. The satellite geometry, link affected adversely, and even with a higher loss propagation performance and overall QoS for Miami are shown in Table 2. model between vehicles, 2.06%, 3.71 %, 2.33% of the listeners Table 3 shows the simulation results for two different have their service rendered unusable. The results show that propagation models. One model assumes a free space path loss the propagation model used for vehicle-to-vehicle exponent of n = 2, and a 10 dB attenuation factor, with a transmissions has a primary impact on the resulting shadowing standard deviation of 4 dB, whereas another model interference statistics. assumes a path loss exponent of n=2.18, a 16 dB attenuation factor, and a 4 dB standard deviation. REFERENCES [I] R. Akturan, "An overview of the system," VI. CONCLUSION International Journal of Satellite Communications and Networking, Special Issue: Special issue on Mobile Satellite Radio, vol. 26, issue 5, This paper has analyzed potential interference to satellite pp. 349-358, 9 July 2008. receivers by making reasonable engineering judgments in [2] L. Cheng, B. Henty, D. D. Stancil, B. Fan, and P. Mudalige, "A fully order to deduce the levels of OOBE that would be seen from mobile, GPS enabled, vehicle-to-vehicle measurement platform for adjacent service WCS subscribers in the SDARS band. In characterization of the 5.9 GHz DSRC channel," IEEE Antennas and doing this work, we sought to determine reasonable guidelines Propagation Society International Symposium, pp. 2005-2008, Honolulu, HI, June 2007. from which suitable spectrum masks could be developed. The [3] J. Turkka and M. Renfors, "Path Joss measurements for a non-line-of­ simulations presented here show how many WCS transmitters sight mobile-to-mobile environment," International Conference on ITS leads to an increase in SDARS receiver noise floor. The , pp. 274-278, Phuket, Thailand, October 2008. simulation statistics provide insights into the exact degree of [4] J. S. Davis, II and J. P. M. G. Linnartz, "Vehicle to vehicle RF this phenomenon by counting the noise floor levels for each of propagation measurements," Asilomar Conference on Signals, Systems, the SDARS receivers as the noise floors are raised by 1, 2, and and Computers, pp. 470-474, October 1994. [5] A. Paier, et al., "Characterization of vehicle-to-vehicle radio channels 3 dB or more. from measurements at 5.2GHz," Wireless Personal Communications, vol. 50, no. I, pp. 19-32, July 2009. TABLE III. SIMULATION RESULTS OF INTERFERENCE FROM WCS MOBILE [6] T. Tank and J. P. M. G. Linnartz, "Statistical characterization of Rician TRANSMITTERS IN MIAMI, FL multipath effects in a mobile-mobile communication channel," FCC Mask 70dB Mask 75dB Mask 80dB Mast' International Journal of Wireless Information Networks, vol. 2, no. I, n=2.0, n=2.18, n=2.0, n=2.18, n=2.0, n=2.18, n=2.0, n=2.18, pp. 17-26, January 1995. IX= lOdE r=J6dE r=JOdE r=J6dE X=JOdE X=l6dB IX=JOdB r=J6dE [7] A. Paier, et al., "Car-to-car radio channel measurements at 5 GHz: Worst Case Pathloss, power-delay profile, and delay-Doppler spectrum," IEEE Outage 10.66% 3.71% 3.27% 1.03% 1.56% 0.40% 0.72% 0.11% International Symposium on Wireless Communication Systems, pp. > 1% 224-228, October 2007. Worst Case [8] Sirius XM Ex Parte Submitted to the FCC in WT Docket No. 07-293, Outage 8.78% 3.02% 2.52% 0.77% 1.19% 0.28% 0.50% 0.06% February 27, 2008. >2% [9] WCS Coalition ExParte Submitted to the FCC WT Docket No. 07-293, Link May9, 2008. Degradation 17.85% 6.54% 2.37% 3.42% 1.89% 7.13% 1.17% 0.50% [10] WCS Coalition ExParte Submitted to the FCC WT Docket No. 07-293, >!dB August 1, 2008. Link [II] J. Goldhirsh and W. J. Vogel, Handbook of Propagation Effects for Degradation 13.44% 4.86% 4.38% 1.48% 2.15% 0.65% 1.12% 0.21% Vehicular and Personal Mobile Satellite Systems, Chapter 3.3, Johns >2d8 Hopkins University and The University of Texas at Austin, December Link 1998. Degradation 10.66% 3.71% 3.27% 1.03% 1.56% 0.40% 0.72% 0.11% > 3d8