Connecting Shoppers With Smart Networks
Since the emergence of suburban shopping centers in the 1950s in the United States, shopping malls have become the predominant form of retail destinations globally. Initially, these malls started as open-air retail hubs. Still, it soon became apparent that there was a demand to protect stores and shoppers from weather conditions. Consequently, the concept of enclosed shopping centers was conceived.
Some shopping malls are designed with large exterior windows that allow ample natural light to enter. For those malls with opaque external walls, a glass-covered opening in the roof, often referred to as a “sunroof,” is incorporated to provide natural light. While a few shopping malls have multi-level parking structures attached to them, most rely on open-air surface parking lots adjacent to the mall, offering little protection from the elements. Small retail stores are typically arranged around the perimeter of these enclosed malls, leaving the central area open for pedestrian traffic.
Today, shopping malls offer more than just shopping options. Many include standalone restaurants and bars, a food court, a movie theater, a gym, a skating rink, and various entertainment facilities. Shopping malls have become central hubs of social life in suburban areas, and visitors now view wireless connectivity as a crucial aspect of their mall experience. Mall management recognizes this importance and places value on implementing an in-building network to deliver superior wireless coverage and quality throughout the mall premises.
The Challenge
In this case study, our subject shopping mall is a two-story enclosed structure featuring concrete outer walls and a glass sunroof. The mall stretches 200 meters in length and up to 60 meters in width. It houses three prominent anchor retail stores, each with separate entrances accessible from the open-air parking lot and numerous small retail shops that can only be accessed inside the mall.
Despite the parking lot enjoying satisfactory signal reception from nearby macro cells, mall management has received numerous complaints about signal coverage and quality within the mall itself. In response to this issue, mall management seeks to install an indoor wireless network to enhance the overall customer experience. This network must accommodate three major wireless service providers (WSPs) and facilitate First Responders’ (E911) signals. It’s worth noting that installing a Wi-Fi network is not required, as one has already been implemented. Additionally, the management prefers to use inconspicuous and minimalistic antennas, avoiding any interference with the mall’s interior aesthetics.
The Solution
To accommodate the diverse range of technologies and frequency bands required, the in-building network is expected to incorporate a neutral-host Distributed Antenna System (DAS) to accommodate the diverse range of technologies and frequency bands needed. In adherence with customer proximity concerns and compliance with International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines, which aim to restrict exposure to time-varying electromagnetic fields, the network will utilize low-power DAS remote units.
In this context, “low transmit power” is defined as a maximum of 24 dBm composite transmit power per amplifier. This approach ensures the network operates within safe electromagnetic exposure limits while efficiently serving the diverse wireless service providers and First Responders’ communication needs within the mall.
Design Requirements
RF Coverage
Given the presence of a glass sunroof in the mall, residual macro signals may exist in the mall’s center. To establish in-building signal dominance in a situation like this, the in-building signal must be 5 to 7 dB stronger than the residual macro signal.
The coverage requirements encompass all common areas and accessible retail shops on both mall levels, excluding the already sufficiently covered outdoor parking lot. Handoffs between the in-building and macro networks will be confined to specified mall entrance areas. Ensuring comprehensive trunked radio coverage, including back hallways and stores, is a critical mandate, while cellular technologies must achieve a target coverage of 95%. Additionally, the in-building signal strength should be at most -100 dBm when measured from a point 30 meters outside the mall.
RF Coverage is required for the following technologies:
- UMTS
- LTE
- Trunked Radio
The following frequency bands must be integrated into the network:
- SMR band (800 MHz)
- Cellular band (850 MHz)
- PCS band (1900 MHz)
- AWS band (2100 MHz)
Target signal strength:
- UMTS CPICH = -85 dBm
- LTE RSRP = -95 dBm
- Trunked radio Rx = -95 dBm
Antenna Placement Restrictions
In common areas of the mall, where antennas are placed, mall management insists on the antennas being as small and inconspicuous as possible to preserve the aesthetic appeal of the mall interior. This requirement excludes back hallways, access docks, freight elevators, and similar areas.
Additional considerations for antenna placement are:
- Antennas are strictly prohibited from being installed inside any stores, including anchor stores.
- Antennas must be shared by both Wireless Service Providers (WSPs) and First Responders.
Best Practices
Antenna Choice and Placement
Two essential requirements govern the selection of antennas for this network. Firstly, antennas must be mountable flush against the wall while maintaining a compact form factor. An ideal choice for such criteria is the omnidirectional Andrew Cell-Max™ O-25 antenna, boasting 0.85 dBd of gain, a V-plane beamwidth spanning 40 degrees, and an expansive H-plane beamwidth of 360 degrees. An illustration of an Andrew Cell-Max™ omnidirectional antenna installation is provided as a reference.
Secondly, when mall management mandates complete invisibility of indoor antennas, this demand can be met by installing antennas discreetly behind the ceiling, utilizing a behind-the-ceiling mounting kit.
An example of an antenna suitable for concealed placement is the Galtronics PEAR M4773 omnidirectional antenna.
The second requirement stipulates that while anchor stores are exempt from coverage obligations, an indoor signal should be accessible near the store entrance to facilitate seamless handovers with the macro network. A directional antenna should be affixed in the common mall area, positioned opposite the anchor store, and directed toward the store entrance to meet this condition. An excellent choice for this scenario is the Andrew Cell-Max™ D-25 directional antenna, offering 4.85 dBd of gain, a V-plane beamwidth spanning 60 degrees, and an H-plane beamwidth of 70 degrees. An example of the Andrew Cell-Max™ directional antenna installation is also illustrated for reference.
Detailed RF Coverage Design
The selection of directional antenna locations on both levels aims to optimize coverage within anchor shops while adhering to the requirement that these antennas be placed in common areas. To address coverage gaps, omnidirectional antennas are strategically installed and mounted flush against the ceiling, primarily in front of smaller stores.
Based on the cumulative percentage distribution indicated in the legend, it is evident that the UMTS CPICH signal exceeds -85 dBm in 94.8% of the lower level and 96.2% of the upper level. This analysis concludes that over 95% of the total area maintains UMTS CPICH signal strength greater than -85 dBm, successfully meeting the UMTS design criteria for the AWS frequency band.
Similarly, the LTE RSRP signal strength surpasses -95 dBm in 94.9% of the lower and 96.6% of the upper levels. Consequently, more than 95% of the total area achieves LTE RSRP signal levels greater than -85 dBm, per the design target for the PCS frequency band.
Capacity Sizing
To accurately dimension the in-building network, it is essential to ascertain the requisite number of sectors to accommodate the capacity demands of each Wireless Service Provider (WSP). The determination of these sectors hinges on several factors, including the volume of visitors during the most congested period of the day, commonly referred to as “rush hour,” as well as the mobile traffic patterns specific to each WSP and their respective subscriber penetration rates. The penetration rate represents the percentage of a WSP’s subscribers relative to the overall population.
To start, we will determine the number of visitors during rush hour, which can be obtained from publicly available sources such as the Travel and Leisure newsletter, where annual visitor statistics for the busiest shopping malls in the USA are listed. Alternatively, direct information from mall management can be sought. For this scenario, we assume there are 5,000 visitors in the mall during rush hour.
Additionally, we will consider the requirements of three Wireless Service Providers (WSPs) that will be included in the in-building network:
WSP A:
- Utilizes the Cellular band with 2 UMTS channels.
- Operates in the 700 MHz band with a 10 MHz LTE-FDD channel.
- Possesses a 40% penetration rate, equivalent to 2,000 subscribers.
- HSPA: 20% subscribers (400)
- LTE: 80% subscribers (1,600)
- Voice: 20% UMTS (400), 80% VoLTE (1,600)
WSP B:
- Operates in the PCS band with 2 UMTS channels.
- Uses the 700 MHz band with a 10 MHz LTE-FDD channel.
- Has a 35% penetration rate, which translates to 1,750 subscribers.
- HSPA: 30% subscribers (525)
- LTE: 70% subscribers (1,225)
- Voice: 30% UMTS (525), 70% VoLTE (1,225)
WSP C:
- Operates in the AWS band with 2 UMTS channels.
- Utilizes the PCS band with a 5 MHz LTE-FDD channel.
- Boasts a 20% penetration rate, equating to 1,000 subscribers.
- HSPA: 25% subscribers (250)
- LTE: 75% subscribers (750)
- Voice: 25% UMTS (250), 75% VoLTE (750)
Table 1 (below) provides the duration of the network connection for each service type during rush hour, expressed in milliErlangs (mE) per subscriber, as well as the fixed data rate in kbps. It’s important to note that a subscriber is not limited to a single service type attempt per rush hour – instead, they are expected to utilize or attempt to utilize all the service types listed.
Compared to other large venues (e.g., stadiums), shopping mall subscribers are generally not inconvenienced by excessive crowd noise. Additionally, unlike subway commuters who often feel compelled to maintain silence in crowded environments, mall visitors do not experience the same social pressure. It’s also worth noting that video streaming, typically restricted in stadiums, is permitted within shopping malls. These unique characteristics collectively lead to longer average voice and data connection durations in shopping malls than in other public venues. Consequently, mall visitors consume significantly more data, establishing them as some of the heaviest data users among patrons of various public locations.
Data Capacity Sizing Example
To assess HSPA and LTE SINR coverage throughout the mall effectively, it’s essential to segment the SINR (Signal-to-Interference-plus-Noise Ratio) into distinct intervals based on the achievable Modulation and Coding Scheme (MCS) within each SINR range. The illustrative example in Table 2 demonstrates that within the region where LTE PDSCH SINR exceeds 20 dB, it becomes possible to employ 64-QAM modulation with a coding rate of R = 0.93. This configuration yields a spectral efficiency of 5.5 bit/s/Hz. For SINR falling between 15 and 20 dB, the spectral efficiency reduces to 3.9 bit/s/Hz.
Likewise, with SINR ranging from 9 to 15 dB, the spectral efficiency stands at 2.4 bit/s/Hz, and so forth. This breakdown allows for a more precise evaluation of network performance based on SINR levels and the associated modulation and coding schemes.
Estimating the number of sectors at the mall can be based on SINR (Signal-to-Interference-plus-Noise Ratio) coverage and call blocking rates for each service type. Generally, for a multi-sector In-Building System (IBS) at a shopping mall, it’s reasonable to assume that the SINR > 20 dB range covers approximately 25-35% of the total area, while the other three SINR ranges are distributed relatively evenly.
Call blocking refers to the percentage of data connections that experience excessive delays. Acceptable call blocking rates are typically under 10% for low data rate applications like voice, email, and web browsing and fall within the range of 10-20% for high data rate applications such as data downloads and video streaming.
The venue sectorization calculation is presented in Table 2, providing a structured framework for determining the number of sectors required based on SINR coverage and call-blocking rates for various service types.
The decision of how to connect antennas to form a sector is crucial, as an incorrect approach can lead to the degradation of SINR (Signal-to-Interference-plus-Noise Ratio) coverage, thereby reducing the maximum achievable data rate coverage within the venue. Let’s examine two sectorization plans in this context: horizontal and wedge configurations.
Choosing between these sectorization plans will significantly impact the network’s performance, and it’s important to carefully assess their implications to ensure optimal coverage and data rates within the venue.
The first sectorization plan assumes strong vertical signal isolation between the floors. However, many malls feature openings in the middle, which can create Line of Sight (LOS) conditions between numerous antennas on both floors. This is contrary to the assumption of effective isolation that we initially made.
The second sectorization option, called the “wedge” sectorization, involves grouping antennas from different floors into a single sector, as illustrated in Figure 15. This approach considers the potential LOS conditions in the mall’s common walking area and seeks to optimize signal coverage and isolation under such circumstances. It’s a strategic choice to address the mall’s architecture’s specific layout and signal propagation challenges.
This plan assumes that vertical overlap containment takes precedence over horizontal containment, typically for malls with openings in the middle.
Let’s evaluate the Maximum Achievable Data Rate (MADR) coverage for both sectorization plans. The MADR coverage map has been computed assuming a 2×2 Multiple-Input Multiple-Output (MIMO) configuration. This map offers insights into the maximum data rates achievable across the venue under this specific sectorization approach.
The analysis reveals that the horizontal sectorization plan yields an average 2×2 MIMO Maximum
Achievable Data Rate (MADR) of 14.9 Mb/s on Level 1 and 15.9 Mb/s on Level 2. Given that the maximum data rate of 58 Mb/s is only attainable close to an antenna, it becomes apparent that the data rate coverage provided by this plan is relatively poor.
Further examination of SINR (Signal-to-Interference-plus-Noise Ratio) coverage confirms that extensive interference in the middle of the mall significantly degrades SINR, consequently impacting MADR. Therefore, horizontal sectorization is not an optimal choice for this type of mall, as it fails to deliver satisfactory data rate coverage due to interference issues in the common walking area.
A cursory visual assessment indicates that the maximum data rate coverage, represented in purple, extends over a considerably larger area when employing the wedge sectorization approach. The average Maximum Achievable Data Rate (MADR) further corroborates this, revealing an average MADR of 31.2 Mb/s on Level 1 and 31.4 Mb/s on Level 2. This data rate is twice as fast as what was achieved with the horizontal sectorization. Consequently, wedge sectorization emerges as the preferred sectorization method for this particular type of shopping mall, characterized by an opening in the middle.
Coverage Plots
The LTE RSRP, 2X2 MIMO MADR, SINR, and 2X2 MIMO coverage plots have been previously presented in the previous four figures. In addition, the critical coverage plot of utmost significance is the “best server plot,” which is depicted in the figure below. This plot provides essential insights into the network’s performance, particularly concerning identifying the optimal server or access point that delivers the highest quality signal to users within the mall.
Implementing a dedicated in-building wireless system is imperative in the case of a large two-story shopping mall with deficient existing macro signal coverage. This network must cater to three Wireless Service Providers (WSPs) and include provisions for the First Responders’ (public safety) network. These WSPs support UMTS and LTE technologies across cellular, PCS, and AWS bands, necessitating the adoption of a neutral-host Distributed Antenna System (DAS) as the solution. Given the mall’s two-level structure, a comprehensive three-dimensional venue modeling is essential for effective network design.
Notably, aesthetic considerations play a pivotal role in DAS design for shopping malls, more so than in many other public venues. A standard requirement mall management sets is prohibiting antenna installation inside any store. To address this restriction, directional antennas enhance signal penetration within all stores. Furthermore, these antennas must be visually appealing and seamlessly blend into the mall’s surroundings. Ideal choices to meet these aesthetic requirements include the Andrew Cell-Max™ O-25 and D-25 antennas.
Given the need for the DAS to serve multiple in-building base-station sectors, a sectorization plan must be developed for each operator. This plan should prioritize minimizing DAS sector overlap, as interference tends to be most pronounced along sector boundaries. In this specific scenario, a wedge sectorization plan is chosen, as it effectively reduces sector overlap on both mall levels.
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