Remote Radio Head (RRH) A new design in base station architecture that separates a cell site base station’s RF and baseband functions for improved efficiency.
Traditional design of cellular installations – antenna towers and their adjacent base stations – places the transmitting and receiving components in climate-controlled cabinets or shelters, connected to the antenna arrays via coaxial cable (figures 5.1 and 5.2).
5.1 Typical cell site architecture, no RRH 5.2 Typical cell site application, no RRH
1900 / 2500
Base Station Baseband Unit + RF Transmit and Receive
Antenna
Base Station Baseband Unit +
RF Transmit and Receive Functions
Power and Battery Backup
Cable mounting brackets jumper cables
for 4 branches 2 radomes per sector
4 coaxial cables shown for alpha sector
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In these configurations, equipment for multiple sectors of antenna coverage share space in the site equipment racks, performing all the functions required to operate a multiple-service, multi-sector cell site, such as:
• Line interfacing
• Backhaul connectivity
• Baseband signal processing
• Power amplification
• Frequency filtering
As cellular technology has grown more sophisticated in the ways voice and data are managed across the network, the overall power requirements for base stations have inched steadily downward. At the same time, advancements in amplifier technology have moved power efficiency for these stations upward, resulting in fewer power stages required in a given base station. And, of course, network providers and service operators have always sought less expensive ways to deliver quality connectivity to their customers.
The new thinking in base station design, embodied in the remote radio head, reflects the emerging realities that drive all of these trends, improving efficiency and reducing operational costs. The difference is in the “distributed base station” concept, which separates the baseband signal processing unit, or BBU, from the RF front-end equipment, collectively called the remote radio head (figure 5.3).
5.3 The RRH is compact and rugged for versatile placement
CommScope: Understanding the RF Path
The RRH contains all RF functionality, such as the transmit and receive functions, filtering, and amplification in a single weatherized outdoor module (figures 5.4 and 5.5).
5.5 Typical RRH cell site application
5.4 Typical RRH cell site architecture
1900 / 2500
COM DIPLEXER 1900 2500
COM DIPLEXER 1900 2500
COM DIPLEXER 1900 2500
COM DIPLEXER 1900 2500
T/R1 T/R2 T/R3 T/R4 RRH-1900 CDMA/LTE
T/R1 T/R2 T/R3 T/R4 RRH-WiMAX/LTE
SPM
BBU
eNodeB Battery
and AD/DC
4 branch RRH per sector jumper cables
for 4 branches 2 radomes per sector
Hybrid fiber/
power cable
AC power from utility
Wired backhaul
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As a bonus, an RRH system can also provide advanced monitoring and control features that allow operators to optimize performance from a remote, centralized location. It allows the operator to monitor and control the remote electrical tilt (RET) of antennas and other functions outlined by the Antenna Interface Standards Group (AISG). An RRH can also remove the need for tower-mounted amplifiers (TMAs) if it is installed at the top of an antenna tower.
Because they are passively cooled, RRHs don’t require fans and blowers that can fail over time. And since they are connected to their corresponding BBUs via fiber-optic interfaces, distance between the two units is not a practical concern. This flexibility means the RRH solution offers several mounting alternatives, including:
• Top of the antenna tower
• Bottom of the antenna tower
• Rooftop mounting
• Wall and post mounting
With the option of locating the RRH near the antenna, transmission line losses can be reduced. Plus, this degree of mounting flexibility makes it easier to implement, and offers more ways to remain compliant with local zoning ordinances – major advantages for this kind of deployment or upgrade.
In order to promote standardization and interoperability, major RRH manufacturers have jointly created a common protocol for communication between the BBU and RRH. This protocol is known as the Common Public Radio Interface, or CPRI. This standard governs the BBU-to-RRH optical interface in RRH applications.
Further standardization is achieved through the Open Base Station Architecture Initiative, or OBSAI. The OBSAI was originated in 2002 by Hyundai, Nokia, Samsung, and ZTE with the objective of creating an open market for standardized base station functional blocks. The standard defines four primary base station functions and designates them as Reference Points RP1, RP2, RP3, and RP4 as follows:
RP1: Communication and control RP2: Transport to baseband interface
RP3: Baseband to RF interface (baseband to RRH for RRH applications) RP4: Power interfaces
The reference point RP3 governs RRH interfaces and serves to promote open standards and competition in the RRH market.
Putting the power where it’s needed
In our competitive cellular marketplace, every dollar and every watt count. And, as always, necessity has proven to be the mother of invention – or at least innovation. The remote radio head architecture represents a new way of thinking about how power is used at thousands of cell sites across the world. It’s an exciting step forward for CommScope and everyone who takes a deep interest in making the networks of today and tomorrow work even better.
Chapter 5 summary Remote radio heads (RRHs):
• A new way of configuring a cell site’s base station equipment
• Driven by efficient new antenna and amplification advances RRH advantages:
• No active cooling required
• Lower overall transmission power loss
• Nearly invisible form factor
• Replacing coaxial cable with RRH means less weight on the tower
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