IEEE Circuits and Systems Magazine - Q3 2019 - 40

Practical Algorithms and Their Computing
Requirements
One of the crucial aspects in practical implementation
is the complexity and computing requirements. The algorithm's complexity aims to measure how effectively
the algorithm uses certain basic resources; time, space,
and energy [22]-[27]. It's essential to find out the complexity of an algorithm in the early phase of development to avoid selecting too complex algorithms, which
could lead to difficulties in later phase (maintainability,
scalability etc.). Traditionally, the complexity of the algorithm has been measured by three metric categories;
space (i.e. number of operations), time (i.e. length of execution time), and energy (amount of consumed energy).
We have reviewed algorithms in each application category in Table 1, summarizing computing requirements and
providing additional information and references.
Improving Performance of Cellular Networks
General Model
Dynamic time-domain operation has an important role in
all database-based spectrum sharing scenarios. Both LSA
and CBRS systems use spectrum databases to control

Sensor
Commander

Spectrum database including the
status of spectrum use in the area
of interest.
-Identification, Location, Antenna
parameters, transmission power,
used channels etc. of CBSDs.

Network consisting of commercial
LTE-Advanced compliant base
stations at 3GPP spectrum band
42 (3.4-3.6 GHz).

Radar Sensing System

Intelligent algorithm to optimize
channel allocations for CBSDs. The
basic idea is to minimize the number
of channel changes while
maximizing the used bandwidth.

Spectrum Access System
SAS Repository

ESC

CBSD Manager

SAS Algorithm

Environment Sensing
Capability = Spectrum
Sensing

CBRS Domain Proxy

SAS
Elements
SAS-User Interface

Managing intermediary network
component between SAS and a
number of CBSDs. Two main
functions: 1) communication
directly with SAS using defined
protocols and 2) communication
with operator controlled CBSDs
using the network management
system.

dynamically 3rd Generation Partnership Project (3GPP) mobile networks. Our measurements have shown that with
current cellular equipment, the timescales of operations
are quite slow. For example, in the implemented CBRS
system [8] shown in Fig. 3, a frequency change from a
band to another one including evacuation of the current
one took several minutes in a field trial. The shown CBRS
system is a three-tier system where the incumbent users
have the highest priority, priority access (PA) users are
licensed secondary users, and the lowest tier includes
the unlicensed GAA users. The low tier users are not allowed to interfere with naval radars nor the fixed satellite
receivers operating in the same 3.5 GHz band.
Radar detection is performed with spectrum sensing
while protection areas are defined for satellite receivers
and these areas are stored in the database. Detailed analysis of the steps in the evacuation and frequency change
processes in [8] show that reconfiguration time is dependent on multiple factors. The network management
system is one of the main causes for slow operations.
Others include the messaging protocol, allocation algorithm related delays, and the fact that current base stations called CBRS devices (CBSDs) in the implemented
system are not designed for fast frequency changes.

Network Management System
PA
LTE 3.5 GHz Test Network

Priority
Access
GAA

CBSD-1

CBSD-2

CBSD-3
With Functionalities
From Domain Proxy

General
Authorized
Access

Figure 3. Field trial environment of the CBRS system in Finland [8].

IEEE CIRCUITS AND SYSTEMS MAGAZINE

THIRD QUARTER 2019

IEEE Circuits and Systems Magazine - Q3 2019

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