# A Review on Recent Advancements in FOREX Currency Prediction
## 1 Introduction  
The foreign exchange market, also known as FOREX, is the world's biggest currency exchange market [1] with over $5.1 trillion of volume trade per day [2]. It is considered to be very complex and volatile, and is often compared with the black box because of the unknown nature and high fluctuation in currency rates [3]. In the FOREX market, currency trading occurs 24 h a day [4] but the trading time is divided into four major time zones [5]. These time zones are the Australian zone, Asian Zone, European Zone, and North American Zone. Each of these zones has its own opening hours and closing hours. Currencies are traded in pairs and most traded currencies are priced against the USD [2]. Based on this trade, the foreign exchange market is divided into three different categories: majors, cross-rates, and exotics [6]. Majors are the most traded currencies which are priced against the USD and occupy the majority of the FOREX market. Cross-rates are the currencies that are priced against a currency other than the USD. The last category, exotics, includes all other currencies that are not major but are priced against the USD. Each currency pair has its own opening price, highest price,lowest price, and closing price based on the trading session. For security reasons, it is not possible for one person to directly go to, register with, and buy from the FOREX market. A person needs to use a third party, also known as a broker, for buying currencies from FOREX. Brokers are people or companies that have access to the FOREX market and are able to purchase currencies directly from there. In the FOREX market, a person has only two options available, either buying currencies or selling if they have brought any currencies previously. If the selling rate of the currency is larger than the buying rate, it results in profits for the person. However, like the share market, the FOREX market is also dependent on events that affect the economy of a country. That's why traders need to know the behavior of the market before they do their trading.  
Recent years have seen a lot of research interest in the FOREX market currency rate prediction. Many researchers have come up with a lot of unique ideas using machine learning for accomplishing this task. Apart from machine learning, many researchers even used the Internet-of-Things (IoT) for estimating rates of different sectors. Such models were used by [PERSON], [PERSON], and [PERSON], who used IoT for estimation of a European barrier price [7] and determining the fluctuation and also for estimating the simultaneous buying and selling prices [8]. From statistical to deep learning, different models along with hybrid models have arisen on this occasion. Not only are these models diverse, but they are also different from each other. It is also quite a tough task to find which model is better among them, but a shortlist can be made by analyzing each of these models.  
In this research, we tried to review the machine learning methods that have been applied in the previous three years, from 2017 to 2019, for FOREX currency price forecasting. The remainder of the paper is arranged as follows. Section 2 includes the interests of the study, Section 3 presents the conceptual framework, and Section 4 discusses the data and methodology that we used. Section 5 presents the classification of the paper. Section 6 includes reviews based on different machine learning approaches. Section 7 discusses the research gaps and future directions. Finally, Section 8 concludes the present study.