**11. Comparison between GPS and GLONASS**

This section gives a brief comparison of GPS and GLONASS. It is essential to understand the similarities and differences between both GPS and GLONASS in particular when combining them in one navigation service or solution. Major differences between both systems are related to the constellation structure, the reference time system, the coordinates system, and the signal modulation or multiplexing technique. The following subsections briefly describe the GPS and GLONASS time and coordinate reference systems.

#### **11.1. Time reference systems**

Both GPS and GLONASS have their own time systems; thus, it is not straight forward to make time transformation from GLONASS time into GPS time or vice versa. The most important factor one must account for when processing data from a combined GPS and GLONASS is the difference between the two time scales.

#### **11.2. GLONASS time system**

As can be seen in **Table 2**, the daily satellite clock stability for GLONASS, GLONASS-M, and GLONASS-K is better than 5 × 10−13, 1 × 10−13, and 5 × 10−14, respectively. The time shift between GLONASS time and the National Reference Time UTC (SU) is 3 h ICD (2008):

$$t\_{\text{c2.00488}} = t\_{\text{uITOS50}} + 0 \text{\textdegree } 00 \text{mins} \tag{5}$$

The following expression is used to align GLONASS satellite ephemeris at one instance with measurements given in UTC(SU):

$$t\_{\text{collMASS}} = \; t + \pi\_c + \pi\_n(t\_b) - \gamma\_n(t\_b)(t - t\_b) \tag{6}$$

where

**10.6. GLONASS navigation message**

**Figure 8.** L3 CDMA signal spectrum [23].

134 Multifunctional Operation and Application of GPS

timing, and planning observations [22].

along with ephemeris and other parameters.

**11. Comparison between GPS and GLONASS**

the GPS and GLONASS time and coordinate reference systems.

eters [22].

The navigation message contains immediate and non-immediate data. It is broadcast from GLONASS satellites at a rate of 50 bps to provide users with necessary data for positioning,

The immediate data contains information about GLONASS satellites. It is broadcast of a navigation signal which includes mainly the enumeration of the satellite time and the difference between the onboard time scale of the satellite and GLONASS time. The difference between the carrier frequency of the satellite signal and its nominal value is also included in this data

The non-immediate data, on the other hand, contain information about almanac of the system. Almanac data provides information about the status of all satellites in the current constellation, coarse corrections of the onboard timescale for each satellite with respect to GLONASS time. Almanac data also have information about the orbital parameters of all satellites (orbit almanac) and correction to GLONASS time with respect to UTC (SU) and some other param-

This section gives a brief comparison of GPS and GLONASS. It is essential to understand the similarities and differences between both GPS and GLONASS in particular when combining them in one navigation service or solution. Major differences between both systems are related to the constellation structure, the reference time system, the coordinates system, and the signal modulation or multiplexing technique. The following subsections briefly describe


GLONASS-M satellites transmit the difference between the GPS and GLONASS time scale (which is never more than 30 ns) [22].

#### **11.3. Time transformation**

GLONASS time could be transformed into GPS time using the following formula [27]:

$$t\_{CPS} = t\_{GLONASS} + \tau\_c + \tau\_u + \tau\_g \tag{7}$$

where

$$
\pi\_c = \pi\_{\text{UTCSD}} - t\_{\text{GLONASS}} \tag{8}
$$


**Table 3.** Comparison between GPS and GLONASS.

$$
\pi\_u = t\_{\rm{urcc}} - t\_{\rm{urcc}\rm{os}\rm{uo}} \tag{9}
$$

• Increased satellite observability

GLONASS and GPS:

**13. Conclusion**

**Author details**

Mohamed Tamazin<sup>1</sup>

Canada

**References**

• Remarkable increased spatial distribution of visible satellites

• Reduced horizontal and vertical dilution of precision (DOP) factors

• The different aspects of the GLONASS and GPS navigation data

and GPS highlighting advantages of combining both systems together.

, Malek Karaim<sup>2</sup>

Technology and Maritime Transport (AASTMT), Egypt

\*Address all correspondence to: malek.karaim@queensu.ca

• The time scale offset between GLONASS and GPS

On the other hand, the next considerations should be accounted for when combining

GNSSs, Signals, and Receivers

137

http://dx.doi.org/10.5772/intechopen.74677

• The differences between the reference coordinate systems used in GLONASS and GPS

The demand for GNSS services and applications has been rapidly increasing. Luckily, we have more accessible GNSSs providing better functionality and broader coverage. Among these, GPS and GLONASS are fully functional at the time of writing. In this chapter, we gave a general overview of both systems, discussing the systems structure and signal characteristics, and provided an overview of the new features of GLONASS that intended to rectify the shortcomings of the GPS. The chapter is tailed with a short comparison between GLONASS

\* and Aboelmagd Noureldin2,3

1 Electronics and Communications Engineering Department, Arab Academy for Science,

3 Electrical and Computer Engineering Department, Royal Military College of Canada,

[1] Bradford P, James S. Global Positioning System: Theory and Applications, Volume I. The

American Institute of Aeronautics and Astronautics, Inc: Washington; 1996

2 Electrical and Computer Engineering Department, Queen's University, Canada

$$
\tau\_x = t\_{\rm cps} - t\_{\rm unc} \tag{10}
$$

In combined GPS/GLONASS data processing, the differences between these time scales must be accounted for. Otherwise, systematic errors are introduced that will affect the combined positioning solution.

**Table 3** summarizes vital parameters of GPS and GLONASS that must be considered when combining GPS/GLONASS data processing.
